Just checked my route on Mapmyrun - I've been using a different website to check distances up to now.
Good news is that according to mapmyrun I've actually done 5.49km, not 5k 
Bad news is that I don't know which website to trust 
I'm getting a Garmin.
Lola465, I use mapmyrun and GPS Tracker Lite, they both tell me different things too. Mapmyrun doesn't seem particularly accurate on distance, especially if I look at the route it says I've taken (it has me travelling through houses!).
As I've just started I don't feel I can justify the expense of the Garmin I want because maybe I won't turn out to be the dedicated runner I plan on becoming after graduation. But I have promised myself the Garmin as a present if I keep it up for long enough.
In fact *snap decision made this very moment* I have signed up to run 6km on 15 September in support of breast cancer. If I finish that my reward will be the Garmin.
Do let me know how yours works out.
That'll just give you a third number. 
Arghh Beads - not helpful! Although you did make me chuckle.
I used a garmin for the first time last night (borrowed one from a friend at work) - mainly just to compare it with the endomondo app I've been using.
On the whole they were both keeping the 1k laps within a second of each other, and both ended up in a total distance of 10mtr within each other too - with endomondo being slightly ahead.
As beads says - it will just give you another number to juggle with. best just to stick with one app/kit that way even if it's wrong at least it's consistently wrong.
And well done on the extra 0.49k anyway.
Happy Running
My new Garmin reports the St Andrews Parkrun as 4.86km rather than 5k. But in general it's much more realistic than either my Nike+ or Endomondo.
I guess nothing's perfect ...
Was beginning to love my Garmin forerunner 110 - my present to me for graduating and a great way to spend my first pension ...yeeeehaaaaa. Today, it couldn't find a satellite until I was about 6 minutes into my run ... Took forever to log-on! Maybe aliens have taken all the satellites away? Awwww well, MapMyRun can't do my local ParkRun - cant get a close enough line to the route for it to register.... So I trust the organisers and their orange arrows and signs. The garmin made it just over 5ks last time I used it when we had contact with outer space. Mind you, our local ParkRun seems to allow some wandering away from marker posts, (it crosses open meadows and a canal path, woodland and public parkland etc) so I guess it could be accurate only if one runs exactly where the arrows are planted rather than either side by a few feet ... Cos after approx 5k there could easily be a few metres of variation either way - it's not an Olympic running track! At the end of it all, I'm with Matthew on this one .... Keep using one app/map/watch which works...and even if it isn't 100% accurate distance-wise, at least it'll be consistent with all your other runs, so you'll have something to compare. Happy running - it's getting out there that counts!
Ok, I'm going to keep using mapmyrun for now and calibrate my iPod to it.
And hope for a Garmin for Christmas
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