Short answer: Apple Watch indoor run distance is an estimate. On a treadmill, GPS distance is not available, so Apple Watch relies on motion, calibration, stride, and pace patterns. The treadmill belt distance can be more useful after the workout, especially for pace and split history.
Why indoor run distance can be inaccurate
Outdoor Apple Watch workouts can use GPS. Indoor Run workouts cannot use GPS distance in the same way, because you are running in place relative to the world. Apple Watch estimates distance from wrist motion, sensor data, and previous calibration.
The estimate can drift if your arm swing changes, you hold the treadmill rails, your stride changes with incline, or your recent outdoor calibration does not match your treadmill form.
Common treadmill mismatch cases
- Apple Watch distance is too short: common when arm motion is reduced or stride changes indoors.
- Apple Watch distance is too long: can happen when motion patterns do not match the actual belt pace.
- Kilometers and miles mismatch: double-check the treadmill unit before entering the corrected distance.
- Intervals feel wrong: if the total distance changes, pace and splits need to be recalculated too.
How to correct the saved indoor run
- Finish the workout on Apple Watch as usual.
- Open Fix My Treadmill on iPhone.
- Select the Indoor Run from Apple Health.
- Enter the treadmill distance exactly as shown on the machine.
- Save the corrected copy and review it in Apple Fitness.
What about future workouts?
Apple Watch calibration may improve over time, but treadmill workouts can still vary. If you care about exact treadmill distance, keep using the treadmill display as the source of truth and correct the saved workout when the mismatch matters.
Related guide
For more detail, see how to fix wrong Apple Watch treadmill distance.
Try it: Fix My Treadmill includes 3 free fixes, then offers a one-time unlock for unlimited corrections. Download it on the App Store.