How accurate is a GPS speedometer?

There is no single accuracy figure for every phone and environment. Signal conditions, device hardware and location-fix timing affect speed estimates.

Why does GPS show speed when I am standing still?

Small errors in estimated position can look like movement. Wait for a better signal and judge a sequence of readings, not an isolated number.

Is the highest recorded speed always real?

No. A poor GPS fix can create a spike. Check the surrounding graph and route before interpreting a maximum reading.

Open Road

GPS Speedometer Accuracy: What the Reading Can Tell You

A GPS speedometer estimates movement from your device location. It can be useful on an open road with a steady signal, but it is not a calibrated instrument. Reception, device hardware and the timing of fixes all affect the reading.

Free to download. Open Road Pro is optional, with a 3-day trial on the yearly plan.

Open Road saved-drive speed graph and speed distribution — A real saved-drive analysis screen. The example readings are not an accuracy benchmark.

Why speed changes when the car does not

A phone receives location fixes over time. Where the device supplies a speed value, our online tool uses it; otherwise the tool estimates speed from the distance and time between fixes. A poor position estimate can therefore become an odd speed estimate.

A sharp change beside tall buildings, under a roof or after a tunnel can be a signal problem. A single maximum value is especially sensitive to a bad fix. Do not treat a lone spike as proof of the speed you reached.

Make a useful comparison

Set the phone up while parked, with location enabled and a clear view of the sky. If you compare readings on a journey, have a passenger watch the display. Compare a stable stretch over several readings rather than one number during acceleration.

The phone, vehicle dashboard and a navigation display can refresh at different times. A difference between them does not establish which device is correct. This guide does not provide a calibration tolerance for your phone.

Read the saved drive in context

Open Road keeps a recorded route alongside drive stats. The speed graph makes an isolated spike easier to notice than a maximum number by itself. Review the route and signal conditions after parking, rather than chasing a higher peak.

About this guide

Published by Open Road. Updated 2026-11-03. App screens show example recorded drives.

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Questions, answered

How accurate is a GPS speedometer?: There is no single accuracy figure for every phone and environment. Signal conditions, device hardware and location-fix timing affect speed estimates.
Why does GPS show speed when I am standing still?: Small errors in estimated position can look like movement. Wait for a better signal and judge a sequence of readings, not an isolated number.
Is the highest recorded speed always real?: No. A poor GPS fix can create a spike. Check the surrounding graph and route before interpreting a maximum reading.

Keep your next drive

Get Open Road for iPhone or Android. Free to download, with optional Pro. The yearly Pro plan has a 3-day trial.