Why pace instead of speed?
Nobody runs at 12.5 km/h. They run 4:48 per kilometre. So pace gets the big readout here and speed drops to a small line underneath, which is the opposite of every other page on this site.
Press Start and you get live pace, a split for every kilometre, your best pace of the run, distance, moving time and how much you climbed. Switch to mph and everything becomes minutes per mile, splits included.
Why does my pace jump around?
Every runner has watched their pace read 3:30 for a second and known they weren't running that fast. Worth understanding why, because the fix isn't more precision.
Pace is the inverse of speed, and inverses exaggerate. A GPS error of half a km/h is nothing at 100 km/h in a car. At 12 km/h it moves your pace by about twelve seconds per kilometre. Slower still and it gets worse. At walking pace the same error is worth more than a minute.
Add your arm swing, which moves the phone back and forth several times a second, and the raw signal is genuinely noisy. That's why this page uses heavy smoothing by default, and the number still moves. Use the splits for truth and the live pace for feel.
Why is my distance longer than the race?
If you've ever finished a marathon with 42.6 km on your watch, this is why. Courses are measured along the shortest legal line, tight to the kerb through every bend. You don't run that line. You weave through people, take corners wide and cross the road for water, and all of it counts.
GPS adds its own error on top. Between tall buildings the signal bounces, and every reflected fix adds distance you never ran. Under a bridge there's no signal at all, and the straight line drawn across the gap is shorter than the road.
- Expect 1 to 2% over on a road race. A marathon reading 42.6 instead of 42.195 is completely normal.
- Expect worse on a city course with tall buildings, and worse again on twisty trails.
- Expect it to read short on a track. Lane geometry and 400 m laps are finer than one reading a second can resolve.
Getting a better signal
- Wait before you start. Stand outside for twenty or thirty seconds until accuracy settles under ±10 m. Starting on a cold fix ruins your first kilometre.
- Armband beats pocket. It holds the phone still against your body and sees more sky.
- Not on a treadmill. You're not moving over the ground, so there's nothing to measure.
- Open ground is best. A park or a seafront gives much cleaner data than a city grid or a wooded trail.
Pace reference
To work backwards from a goal time, use the running pace calculator. It also predicts your equivalent times at the other race distances.
| Per km | Speed | 5K | 10K | Marathon |
|---|---|---|---|---|
| 4:00 | 15.0 km/h | 20:00 | 40:00 | 2:48:49 |
| 4:30 | 13.3 km/h | 22:30 | 45:00 | 3:09:53 |
| 5:00 | 12.0 km/h | 25:00 | 50:00 | 3:30:59 |
| 5:30 | 10.9 km/h | 27:30 | 55:00 | 3:52:04 |
| 6:00 | 10.0 km/h | 30:00 | 1:00:00 | 4:13:10 |
| 7:00 | 8.6 km/h | 35:00 | 1:10:00 | 4:55:22 |
Frequently asked questions
Why does my live pace jump around so much?
Pace is the inverse of speed, so a small speed error becomes a big pace error. About twelve seconds per kilometre for every half a km/h at running speed. Your arm swing adds more. Turn up the smoothing, and read the splits rather than the live number.
Why is the distance longer than the race distance?
Courses are measured along the shortest legal line and you don't run it. You weave, take corners wide and cross for water. GPS error adds a bit more. One or two percent over is normal.
Can I use it on a treadmill?
No. You're not moving over the ground, so satellites have nothing to measure. It reads zero.
Does it work on a running track?
It runs, but badly. A 400 m lap curves constantly, which is finer than one reading a second can resolve, so distance comes out short and pace is unreliable. Time your laps instead.
How do I switch to minutes per mile?
Tap mph at the top of the page. Pace, splits and every distance follow automatically.
Does it save my runs?
Your current trip survives a reload, but nothing is uploaded anywhere and there's no history. That's the same decision that means your route never leaves your phone.