Your GPS pace jumps because runners move slowly, about 3 metres a second, while a phone or watch only knows its position to within a few metres, and pace magnifies every small speed error. Instant (or current) pace is built from the last few seconds of that data, so it can swing 30 seconds per kilometre or more while your legs do nothing different. Lap and average pace use far more data and are much more accurate. Use instant pace as a rough check that you’re in the right zone, lap pace to hold a target, and average pace to judge the whole run.
How is each pace calculated? #
| Metric | Based on | How steady | Reacts to a change | Best for |
|---|---|---|---|---|
| Instant / current pace | GPS speed over the last few seconds, smoothed | Jumpy | Fast, but noisy | A rough “am I close?” check |
| Rolling pace (some devices) | The last few hundred metres or minutes | Fairly steady | Within a minute or so | Steady runs without laps |
| Lap pace | Time ÷ distance since the lap started | Steady, and steadier through the lap | Slowly late in a lap | Tempo runs, intervals, races |
| Average pace | Total time ÷ total distance | Very steady | Barely | The run summary |
Instant pace comes from the device’s current speed estimate. Phones and watches get it mostly from the Doppler shift of the satellite signals, then smooth it over a few seconds. How much smoothing each brand uses varies and usually isn’t published.
Lap pace is plain arithmetic: time since the lap started divided by distance covered in it. Laps can be automatic (every kilometre or mile is common) or manual, when you press the lap button.
Average pace is total time divided by total distance. Some apps use moving time, which leaves out stops at lights; others use elapsed time. Check which yours shows before you compare runs.
Why does instant pace jump around? #
Three things feed it.
Position noise. At 5:00 per km you move about 3.3 metres per second, and under open sky a phone’s position is only good to a few metres. If an app worked pace out from position changes alone, one bad fix could halve or double it. Doppler speed is steadier, but trees, buildings, a swinging wrist or a bouncing phone still add noise.
Pace magnifies it. Because pace is the inverse of speed, a small speed wobble becomes a big pace swing. Suppose your real pace is 5:00 per km (3.33 m/s) and the speed estimate wobbles by just 0.3 m/s either way. The display swings between about 4:35 and 5:30 per km. At walk breaks it’s worse still, since a tiny speed error at a slow speed is a huge pace error. The pace vs speed conversion guide shows the maths.
Smoothing adds lag. To calm the number, devices average several seconds. When you start an interval, a heavily smoothed instant pace takes a few seconds to catch up, so you speed up more than you need to and go out too hard. It’s also why instant pace often looks slow right after a surge.
Instant pace also struggles wherever GPS does: under trees, between tall buildings, on switchbacks and on the tight bends of a track.
How accurate is lap pace? #
Lap pace is only as accurate as the lap’s distance. If your watch measures a kilometre lap as 1.00 km when you really ran 0.98 km, your lap pace flatters you by 2%. On an open road GPS distance over a kilometre is usually close; on trails, tight courses or downtown streets it can be off by tens of metres per lap.
Short efforts suffer most. A GPS error of 30 metres is 3% of a 1 km repeat but only 0.15% of a 20 km long run. So average pace over a long run is usually close to the truth, while pace for a short interval can be noticeably off. That’s why track sessions and short repeats are better timed against a known distance.
Races show the lap problem clearly. Your auto-laps drift away from the official kilometre markers as the race goes on, because courses are measured along the shortest legal line and you don’t run it: you swing wide at corners, weave past people and drift over for water. Why your GPS running distance doesn’t match the route explains this in detail. The fix in a race is to press the lap button yourself at each marker, so lap pace becomes true split pace against the course.
When is average pace the right number? #
Average pace is the most stable figure and the least useful for pacing in the moment. Early in a run it swings with every change; by the second half it barely moves, so if you start 20 seconds per km too fast, the average hides it for a long time. Where it shines is afterwards, as the honest summary of a steady run and the number to compare against last week’s run on the same route.
Which pace should you watch? #
- Easy and long runs: average pace, or better, effort. Glance at lap pace each kilometre if you like.
- Tempo runs: lap pace. It settles within the first minute of each lap.
- Intervals: lap pace with a manual lap for each rep. Run the first 20 to 30 seconds on effort while the numbers catch up, then check.
- Races: manual laps at the course markers, or elapsed time at each marker against a pace band.
- Hills and trails: effort or heart rate. Pace on a steep climb says more about the gradient than your fitness.
- Track: lap time per 400 m. GPS is weak on tight bends, and the track itself is the accurate measure.
How to get steadier pace numbers #
- Get a fix before you start. Twenty or thirty seconds standing in the open helps more than any setting, especially if the device hasn’t been used for a while.
- Record every second if your watch offers a choice. Battery-saving modes store fewer points and make corners worse.
- Carry a phone where it can see the sky. An upper-arm band or a waist belt beats a pocket or a pack.
- Turn on multi-band GNSS if your watch or phone has it and you run in a city. Receiving two frequencies makes reflected signals easier to reject.
- Use a footpod for track work. It measures stride with an accelerometer rather than GPS, so it works on bends and indoors once calibrated.
- Put lap pace on your main screen, so it’s where your eyes go first.
- Compare like with like. A downtown loop and an open riverside path won’t give comparable numbers, even at the same effort.
Where does a GPS speedometer fit? #
A speedometer app shows speed, not pace. Speedometer GPS displays the phone’s GPS speed averaged over the last five one-second readings, which makes its live number roughly the speed version of instant pace, with the same strengths and limits. It has no laps, no pace display and no auto-pause, so for structured workouts a running app or watch is the right tool.
It also isn’t a good distance counter for runners. It ignores steps of less than 5 metres between one-second fixes to keep a parked phone from adding distance, and nearly all running is slower than the 18 km/h (11 mph) it takes to clear that, so its trip distance reads well short on foot. Its average speed is still sound, since it comes from the receiver’s speed measurement, and average speed × moving time gives a fair estimate. For measuring top speed in strides and sprints, it works fine.
Frequently asked questions #
Why is my GPS pace so inaccurate? #
You move slowly compared with the size of GPS position errors, and pace magnifies small speed errors, so the live number jumps, especially near buildings and trees. Use lap pace over a kilometre or mile instead, and keep the device where it can see the sky.
Why is my instant pace different from my lap pace? #
Instant pace uses the last few seconds of GPS data, while lap pace uses everything since the lap started. A few seconds of noise barely moves lap pace but can swing instant pace by 30 seconds per km or more. When they disagree, trust lap pace.
Should I use lap pace or average pace in a race? #
Lap pace, with manual laps at the kilometre or mile markers. Average pace reacts too slowly to warn you when you’re drifting, and auto-laps drift away from the markers because your GPS distance isn’t the course distance.
Is instant pace useful on a running track? #
Not very. Tight bends are exactly where GPS cuts corners, and you’re moving slowly compared with the position error. Use lap time per 400 m, or a footpod.
Why does instant pace lag when I speed up? #
Devices smooth instant pace over several seconds to stop it jumping, so a real change takes a few seconds to show. Start each rep on effort, then check the number once it has caught up.