What is Peak Flow? : There seems to be... - Asthma Community ...

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What is Peak Flow?

EmmaF91 profile image
EmmaF91Community Ambassador
44 Replies

There seems to be a lot of confusion of what peak flow is, how it works and what is a ‘good’ score so I thought I’d make a post on it!


Firstly peak flow (PF) can also be called peak expiratory flow (PEF) or peak expiratory flow rate (PEFR) so any and all of these abbreviations means the same thing so don’t get confused if people write them differently!

PF is your maximum speed of expiration, so it literally just measures your ability to breathe out. It measures the airflow through the bronchi (large airways) and thus the degree of obstruction in those airways. However it won’t necessarily show restrictions in the smaller airways, and this is why some people have ‘unreliable’ PFs, as their asthma level and PF do not correlate due to their asthma not affecting the larger airways. That being said those whose asthma mainly affects smaller airways will normal have a drop of some description as there is less air in their lungs to breathe out, it just doesn’t meet with the ‘expected’ drop for the severity of attack.

When you use a peak flow meter (PFM) it measures litres per minute, but on spirometry it’s measured per second so anyone with confusion there, times it by 60 and you’ll be able to compare to your usual measurements 😉. There are many different ‘brands’ of manual PFM, as well as child ones (is a lower range). So long as it works and you’re not beating it (ie you have the kids one and your best is out of range 😉) then any is fine! I think mini-wright is the go to for most of the NHS but it really doesn’t matter! There are digital PFMs available, however there is no clear verdict on how good/accurate these are, and I think people often find they score a higher best on digital compared to manual. For this reason, whichever device you decide to use ou should stick to!


Something that’s not always taught, but always commented on! To do it correctly you should do it standing (unless advised against this for other medical reasons), keeping the PFM horizontal (no angling up or down!), with the numbers facing up. Hold at the bottom (making sure to not impinge the moving arrows pathway!) and not the top/end. Take a big deep breath in, create a good seal with your lips on the mouth piece and blow AS HARD AS POSSIBLE! 😉😂 repeat it 3 times (with recovery if you need it) and the BEST score is the one that you count (I knew someone who thought it was the average and would then do more maths! 😅😂).


Asthma is something that’s really hard to diagnose, but one this that is known is the reversibility. For asthma (even those with unreliable PFs) if you are having issues, taking 2 puffs of salbutamol should improve your score. This is known as the reversibility test, and is sometimes carried out in GP practices, as well as hospitals etc (officially its done with spirometry and other tests, but can be done unofficially with PFMs at home). Simply put, you do PF whilst mild-moderately symptomatic, you take inhaler, you wait 15 mins (time it takes for salb to kick in), you redo PF. If you have a big enough improvement it is indicative that asthma may be the issue, if there is little/no improvement it is more likely to be something else.


Best peak flows are personal, and should be used over and above your predicted if you know it. If you don’t know your best you should use your predicted until you’ve worked it out! The current predicted chart I think was produced in the 70s/80s from a town in Scandinavia, so may not even truly represent the average for today anyway. And it is just that... an average! Some people will be way above predicted, others will be way below! There are so many things that can affect your best score, as it will be affected by how large your lungs are. As a random example if your lungs can at max hold 1L of air you will never ever be able to blow out more than 1L, even if your predicted is 1.5L, but if you can hold 3L of air then you should be able to blow out more than 1.5L. Some of the things that can affect your best scores are; gender, height, age, weight, PF technique, standing v sitting, time of day, high level/endurance/frequent sports, playing wind instruments, singing frequently/professionally/in a choir and smoking to name but a few. Factors like sports, music and smoking have a greater effect as a child, so the changes may last into adulthood, however it will affect as an adult too. This is why it’s pointless comparing best PFs as so many factors go into it, and it truly doesn’t represent anything but how big your lung fields are. My friend and I are predicted the same PF, she has no respiratory (or any health) issues and she gets 68% predicted, I have severe asthma and I get 143% predicted! Best scores can also increase and decrease over time (age being a factor 😉), so I think they say your best only counts if you’ve hit it in the last 6 months (I get confused between 6 or 12 but think it’s 6 😅), and you should hit it multiple times to confirm its your best (can be done all on the same day 😉). Those new to asthma often find as they gain control (and practice PF technique) their best also increases... personally I think it took a year before I found my best, and had to change my plan about 6 times 😅. And yes to anyone questioning, when you get a new best, you should then adapt the numbers of when you should seek help!


Everyone should have an asthma action plan (AAP) which should be filled out for you by your GP or asthma nurse. If you don’t have one you can find them here; asthma.org.uk/advice/manage.... Typically asthma plans have ‘zones’; green, yellow/amber and red. They are decided by asthma symptoms +/- PF score (if you have an unreliable PF you go on just symptoms). I am not going to go into symptoms of each zone (as they are written on the plan 😉) but will do peak flow. There is often a slight variety in % as normally the doc writing the plan is doing it individually but typically;

GREEN zone is anything above 70-80% of your BEST score (I use 75 😉)

RED zone is anything below 50-60% of your BEST score (typically it’s 50% but some brittle asthmatics have to use 60%, so don’t worry if that’s what you’re told to do). If you hit red zone you should follow the guide of what to do, and be considering going to hospital, if you manage to resolve it at home with 10 salbutamol puffs as suggested you should follow up with your GP that day or the next. If it’s the weekend, it’s worth contacting 111 for OOHs just to be checked over.

YELLOW/AMBER zone is the area between the two! This is typically when you should contact your GP, and possibly start your emergency pack of steroids if you have them. If you find you are constantly in yellow, and only return to green after reliever medication (MART or salbutamol) and it’s an ongoing issue it may be that you need to change your preventer inhaler or escalate your maintenance treatment with add ins like montelukast.

I also add in BLACK zone which is anything below 33% as that is classed as life threatening so my rules say I HAVE to go to hospital if I hit that, even if I recover with home meds (just wanted to explain why my PFM is green, yellow, red and black).

As you can see above I have added a photo of my PFM, and it usually goes down a storm with any medic who hasn’t seen it 😉. I don’t know about you, but when my asthma’s bad, I REALLY can’t do maths so this was my solution 😅😂😂. It’s easy to do and doesn’t affect the function of the PFM, just get 3 (or 4) sharpie/marker pens and colour in your zones! In times of trouble (or when in hosp with medics who don’t know your best score) it’s easy for everyone - blow and check the colour!!!



Simply put, yes. Yes you should 😅. It is usually advised that you track your score morning and evening, and record them either in an app or on a paper diary as it’s a good way to measure your control over time and see fluctuations and trends over time, and can often help identify a problem before you are even aware of it! When you do it, you should always try to do it at the same time of day and either always before or always after your maintenance medications. You can do it both pre and post if you really want to! If you are new to asthma, or in hospital due to attack, they may ask you to track it during the day, as that helps to see if you are well controlled or not, and can also help diagnose asthma.


I’m talking manual here so the ones you get from the good old NHS 😉. I’m pretty sure they don’t come with any best before date (if they do then comment cause I’d have learn something new! UPDATE Singinglouder says life expectancy is about 3 years 😉), however they do wear out and get old. The internal mechanism can start to break down, which can start putting out weird and random results 😅😂. For me, I know it’s time to replace when, what I think is rubber inside starts to stick, creating a slight popping sound and normally a stupidly good PF (I once ‘beat’ a PFM of 800 due to this happening, when on a different device I was scoring under 300 😅). As soon as it’s happened once, I get organised to get another, and don’t forget you can get them on prescription if you need to!

Here’s a link to the AUK peak flow page asthma.org.uk/advice/manage... which also links further to AAP and PF diaries if you are interested.

And for those who would like to see the most commonly used predicted score chart; peakflow.com/pefr_normal_va... (I REALLY hate they call these ‘normal’ and not predicted scores 🙄😒)

Alternatively If you’re concerned or need advice about anything The AUK helpline nurses are great and can be reached on 0300 2225800 M-F 9-5. Alternatively their WhatsApp service is 07378 606728.

Hope this helps anyone with questions, and if I’ve missed anything please ask and I’ll do my best to answer/add it to the post!

44 Replies
twinkly29 profile image

Thanks Emma - it's awful that so much asthma care doesn't involve people being taught this so I'm glad people here now have the info right there 🤩

A clearly written and comprehensive piece on Peak Flow and PF Meters. It something I was aware of but it is good to be reminded and this is so clearly put.

Asthma treatment and management has changed over the years.

In 1990 age 19, I was diagnosed with asthma by my new GP on going to University. This was done by a comprehensive new patient questionairre screening and based on my answers I was given a Peak Flow Meter and graph and taught to do the 3 readings and record the best. I was asked to do this 3 times a day for a month the GP said based on the graph I had asthma. She pointed out the pattern on the graph.

The GP gave me Ventolin and Becotide and asked me to repeat the Peak Flow for another month after this month was up I stayed on these medications for 2.5 years before had to be changed. Made a major difference in my life having been undiagnosed for 4 years.

Fruitandnutcase profile image

Fantastic! Thank you Emma 😊

Lee2k182 profile image

Great bit of break down there, thank you.

I'm confused though, about the x60 bit.

On my lung function test, pre bronchodilator I blew an FEV1 of 4.1L and my peak flow on the same day was 540.... Those numbers don't add up when I times 540 by 60, it's 3.24L... am I doing something wrong?

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Lee2k182

FEV1 isn’t the same as PEF (what PF usually recorded as on spiro) FEV1 is the forced expiratory volume in the first second, whereas PF is the highest you’ve hit your entire out breath, and so you can’t really correlate FEV1 to a PF, so the x60 doesn’t work. It’s very subtly different 😅. Hope that explains the issue 😅

Lee2k182 profile image
Lee2k182 in reply to EmmaF91

Ah! I see, what a dummy! You'll have to forgive me as I'm a complete novice! I just put 2 and 2 together and made 6! I just thought cos they were both forced breathing that thats what I was converting it to.

Wheezebag profile image

Thanks Emma, you've clarified a few points for me and I've been using a PFM for a good few years.

Singinglouder profile image

Re best before date: my PFM says ‘with careful use the Mini-Wright would be expected to last for three years’.

As long as you remember when you got it...

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Singinglouder

Yeah. That’s what I was thinking when I wrote that also 😂.

But thanks. Good to know life expectancy of them 😉. Tho as I’ve had about 5 fail on my in about 5 years I suspect there may also be a factor on how often you use it 😅😂😂 (maybe normal use or the GP level of use where it’s random will give it 3 years🤷‍♀️😂)

Singinglouder profile image
Singinglouder in reply to EmmaF91

Maybe you’re not being careful enough 😂. (Do wonder how you use it carefully - or even recklessly 😁)

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Singinglouder

😂😂😂- well a couple images used for using PF look like the actor is trying to deep throat it... no comment on how to recklessly use a PF 😂😂😂 (also as a student there was a ‘serious’ discussion on if a fart would have a PF... that I’d class as reckless use cause I bet someone somewhere in the world has tried 😂😂😂😂). I must admit I do tend to just chuck mine about (into bag, drop on floor etc) so maybe that’s why I go through them quickly and it’s not that I just have to use it throughout the day as I previously suspected 😉😂. I obviously need to padded velvet box to store it in 😜

Singinglouder profile image
Singinglouder in reply to EmmaF91

Mine does actually say to keep it in the shaped plastic container it came in - which I’m sure we all do 😁. I’m a bit more careful with my electronic meter, mostly because of the cost, but that just means keeping it in the soft drawstring bag it came with, which doesn’t offer a lot of protection - on the other hand, I’ve just checked, and it’s not long had its fifth birthday, which isn’t bad (only one bit superglued, and it’s not crucial to the function).

Maybe fitted boxes would be a nice business idea for someone - or a silicone case, I’ve got them on everything else I’m likely to drop 😂

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Singinglouder

Yeah. I don’t really use my electronic (I’m notorious for not charging things then it’s useless 🙈) But when I did it was usually packed away more carefully 😅😂😂. TBH I use mine so often I’d expect it to wear out slightly quicker than normal (severe and a dropper not a feeler until it’s too late, so I’m instructed to check when I do get symptoms so that I can the right treatment as I tend to undertreat 🤦‍♀️)

Definitely need someone to create a nifty ‘asthma’ bag for all our asthma needs!

Paradigm profile image
Paradigm in reply to Singinglouder

They come in a plastic container!?

in reply to Paradigm

They can do - I’ve bought one from amazon which has a hard plastic container which folds out to become the handle.

Blue-Breeze profile image
Blue-Breeze in reply to Singinglouder

I've just found my instruction leaflet. It says...with careful use the mini- Wright standard peak flow meter would be exexpected to last for two years (2, 000 uses) Now there use instruction is morning and night.

Leaflet dated May 2019 maybe a change?

hilary39 profile image

Great overview to have in our archives for people who do a search for the term--thank you!

EmmaF91 profile image
EmmaF91Community Ambassador in reply to hilary39

It’s why I did it 😂. Thought as we have so many people ask about PF, having something to signpost to would be helpful 😅😂

Pianoperson profile image

Hi Emma

Thanks for this - v useful

I have been lifelong asthmatic but only recently have had a pF meter (which I decided to buy - never offered one) But I am slightly confused on the zones you mention. You seem to be referring to zones in an action plan - so I wanted to understand the zones on the meter. I bought the meter as my gp was suggesting that my asthma had developed into copd - I am not convinced so I thought I would begin to monitor. In the past - in the surgery at check ups my pF was around 220 - has been for years. With my own pF meter I started (3mths ago) around 180 but now regularly 250 so there is obviously technique involved - however that doesn’t get me out the red zone on the pF meter (and am feeling good - am 65, jog 1.5mls every day + 30mins yoga). So do you just ignore the zones on the meter?

Some insight gratefully received


EmmaF91 profile image
EmmaF91Community Ambassador in reply to Pianoperson

So the zones are personal (the picture is my PF zones, and as I said I have a high best score 😅). If your Best score that you have achieved is 250 (and you are symptom free), then your red zone will be below 50% of that (so under 130), and your green zone (depending on the % you use) will be above 180/190 (75%). Your yellow will be the area between the 2. Your symptoms of asthma +/- your PF helps you work out what your asthma is doing plus how you should respond according to your asthma plan. When you hit new bests you should change your boundaries. As I said PF and boundaries are personal. With COPD (and asthma/COPD overlap) things can be a little bit different, but I only have the knowledge of the asthma aspect. From memory I think COPD can have lower best PFs, and may get less reversibility (Tho will get some!).

I hope that answers your question 😅

Pianoperson profile image
Pianoperson in reply to EmmaF91

Hi that is really helpful - I have never had this explained before

I have been obsessing about trying to get out of the red zone on my meter which would mean me getting 300 which just seemed to be way beyond me which was depressing me greatly

So thank you for clarifying


EmmaF91 profile image
EmmaF91Community Ambassador in reply to Pianoperson

I’m not sure if your meter has the zone arrow things or not (most don’t come with any zones hence the art project on mine 😉) but if it does they should be adjustable for you if that helps. But yes this is one of the reasons I did this post, to hopefully help people understand what it is and how to apply it to them (and not compare to others!).

Pianoperson profile image
Pianoperson in reply to EmmaF91

Ah ha - I have just realised that the zone indicators on my meter move!!!!

So I shall stop puffing like mad trying to get out of the red zone (which was obviously preset when I bought it

What a revelation

Thank you!

Ghoulette profile image

Thanks Emma. Really useful and lots of info xx

CDPO16 profile image

Emma, you should be a specialist teacher with your extensive knowledge and understanding x

Willow7733 profile image

Wow! This is the information I have been looking for. Thank you Emma! I was looking at a digital PF meter, but I think I will save my money and keep the manual one I have. Thank you so much for clearing everything up for me.

Nifflerluck profile image

Brilliant thank you Emma !!

Like a kiplings cake - exceedingly well written!

Thank you.

Casey_87 profile image

Thank you, this is so helpful Iv been doing my peak flow whilst on new inhaler and my peak flow hasn’t changed I’m in the amber category and have been ever since I was diagnosed

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Casey_87

Have you ever been in green zone/hit 100%? If you’re working from predicted that may explain it. Not everyone does get 100% predicted as I’ve said in the blurb. If you have hit 100% it’s worth asking about a short course of steroids. Most inhalers recommend that you dont start them during exacerbation without treating the exacerbation first, as it can take them so long to build up in system and start working.

If you’re currently symptomatic and struggling then that will explain still being yellow.

I hope this helps

Casey_87 profile image
Casey_87 in reply to EmmaF91


Iv never been in the green for the 3 years Iv had asthma. I’m currently getting 350-400, safe to say the doctor I have now is doing all they can to get me better. Because of my profession oral steroids are the last resort have another review Friday they have told me I should be at 500 for my peak flow.

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Casey_87

Should doesn’t always mean it’s possible. As I think I’d said predicted is just an average. My friend and I are both predicted the same 440, she is ‘healthy’ and scores a max of around 300, I have severe asthma and my max is 620/630. If you’ve never hit it even on your best days then it’s probably a situ like my friends where her lungs are just ‘smaller’ than average. Think of it like heart rate. The average is about 70/80bpm, but some people run slower at 40/50bpm and others up at 90/100bpm. Those asymptomatic either higher or lower than average aren’t necessarily sick, however if you focus on average they look it. (I hope this makes sense)

The predicted PF as I said was developed in the 70s/80s in Scandinavia. It stands to reason that it won’t necessarily correlate to today’s world. PF bests are personal not average.

If you don’t have any symptoms you are probably controlled, despite not meeting your predicted. If you’re concerned tho you can always give AUK a call! The nurses are great and can be reached on 0300 2225800 M-F 9-5. Alternatively their WhatsApp service is 07378 606728.

Hope this helps explain things

Claire-Rose profile image

That is such a good idea might have to do that to my peakflows. By the way I’m jealous as your yellow zone is my green 😂

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Claire-Rose

Have fun 😉. I recommend sharpies is they aren’t a trigger for you!

I often wish my best was lower. It would lead to a much easier time in a&e. My 50% scores can be seems as absolutely fine (300) and my 33% (210) as ‘oh maybe a tiny issue’ if I get someone hyper focused on predicted scores... this often leads to bigger issues as I get ignored whilst really struggling.

Claire-Rose profile image
Claire-Rose in reply to EmmaF91

Oh wow I suppose that ain’t good when you’re struggling and the doctors and nurses are focusing on the numbers they see rather than your average peak flow. For me because my peak flow is normally low I never really reach 30% so they don’t take me seriously either

EmmaF91 profile image
EmmaF91Community Ambassador in reply to Claire-Rose

Whereas I can be at 30% and have triage tell me I’m fine. Then have to wait and hope for the ‘right’ nurse to come and spot that I’m in silent chest (hence no wheeze) who then rush me to resus (once this happened after a 1-2hr wait and OTHER patients trying to alert reception about me as they were concerned... another time a doc walked past the waiting area, saw/heard me, in essence had a go that I wasn’t already in resus to receptionist and got me a chair 😅). So much opportunity for poor care in asthma, and for severe asthmatics it doesn’t tend to calm down until they know you and believe you aren’t FII/non-compliant/anxious etc...

Claire-Rose profile image
Claire-Rose in reply to EmmaF91

That is so true I have experienced the same thing before taken to majors by a nurse who didn’t know me or look at my notes ( if they do I go resus as they get scared) the doctor in majors asked me what I was doing here as I’m always in resus and took me to resus for a doctor who didn’t know me to tell me I don’t have a wheeze but gave me 2 nebs anyway as she looked at my notes and got a bit scared 😂 then the medics came and saw me and weirdly enough after the 2 nebs I started to get a wheeze. It’s Amazing how many people don’t have the typical asthma symptoms and it’s usually us with the most severe types

Shezxx profile image

This is great thank you, really need to start this its so cold atm x

mjrminor profile image

Hi Emma,

I've just come across your very comprehensive post. I have moderate asthma but I also have an unreliable PF, as much of my asthma seems to hit the smaller airways. On my good days I can easily hit 800 on the peak flow meter, (big lungs?), yet on bad days (usually triggered by something) when I'm struggling to breathe out and I'm having to use my reliever a lot, my PF rarely drops below 700.

I was diagnosed with adult onset asthma 5 years ago, I've never had an asthma plan until this year, when I moved to a new GP practice and downloaded the plan myself. Even then the asthma nurse kept going on about PF even though mine is unreliable and the meter doesn't shift all that much. My asthma plan still feels a bit sketchy to me because it relies so heavily on PF when I feel like it should rely more on symptoms. Just wondering if you have any advice about how I can better adapt my plan?


EmmaF91 profile image
EmmaF91Community Ambassador in reply to mjrminor

Remember that on the plan it discusses PF OR symptoms as a marker for an issue. You don’t have to have the PF issue to start amber/red zone treatment. Having an unreliable PF does make things more difficult when seeking help for stuff however they should be able to hear issues in your chest (wheeze, quiet patches, silence etc). It’s a pain but there it is. Others who also have unreliable PFs may have more suggestions 😅

mjrminor profile image
mjrminor in reply to EmmaF91

Thanks, Emma. I'll take another a look at my plan again.

Smegs1978 profile image

I’ve just come across your post, and I’m so impressed by your colour system on your peak flow, no idea why I never thought to do something like that.

I have severe asthma but don’t wheeze until my peak flow drops to 30% so generally don’t get the correct treatment quicker enough in a and e. I’ve only ended up in resus twice and thankfully never needed ITU or HDU, however I’ve had lots of admissions (7 since Oct).

My predicted is something like 410 I think, however I can get 510 on a good day, so having the colours on peak flow will be excellent so the drs can see how bad my peak flow is and hopefully treat me appropriately going forward.

virgolizzy profile image

Thanks Emma, never knew about the % & coloured zones & a great idea to mark it on the PF. I have had trouble with my lungs for years & was classed as idiopathic lung disease, but only after a virus pre covid, was I diagnosed with severe asthma. My peak flow is abysmal - my normal is 200 & when my lungs are flaring it’s 150. (my fev1 are also not good 🤦🏽‍♀️). Would the % & related colours still apply for me as in the words of my Consultant, I have very limited capacity. I am assuming if it got lower than the 150, although technically in the amber zone, am I right in thinking that is so dire, I would need to go into hospital anyway? ( I am very fortunate in not having to have to do that as yet 🤞) When asking about my asthma plan - the Consultants asthma nurse, just shrugged her shoulders & said if it gets too low just ring an ambulance. So I am just relying on my common sense really.

bluecar15 profile image

This is such a comprehensive explanation and I love that you've actually explained not fitting the chart & peakflow not showing the small airways. Thank you!!! With standing for the peak flow- I understand the main thing is consistency? I get majorly dizzy/ lightheaded from a peak flow (is this normal I never see it mentioned) so I get told to take it sat down but I do worry about accuracy. They say its fine as long as I sit down each time? The other thing I'm always unsure about, after I've taken the big exhale I can force out a bit more air which pushes the meter higher, the nurse always makes me do this but it was my understanding that the meter is supposed to be measuring one exhale? I'm not breathing in between but surely it still counts as 2 exhales as that last bit is probably residual air that on a usual breath would stay there right?

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