GPS Odometer: Measure Trip Distance

How the GPS odometer works

Each time your phone gets a new GPS position, about once per second, the odometer measures the straight-line distance from the previous position and adds it to your trip. Over a journey those small steps add up to the total distance travelled, following every bend in the road rather than the shortest route between two points.

The distance between two fixes is calculated with the Haversine formula, which accounts for the curvature of the Earth. Movement that falls inside the GPS margin of error is treated with care, so standing still does not quietly add metres to your trip.

What you can measure

• Driving: check a route length, compare it with your car's trip meter, or log the distance for mileage claims.
• Cycling and running: see how far you have gone without a bike computer or sports watch.
• Walking and hiking: measure a dog walk, a trail or your daily loop.
• Train and bus journeys: watch the kilometres tick by on a long trip.

Tips for an accurate trip distance

Start the odometer outdoors and wait for the status to show Tracking before you set off. Keep the page open and the screen on; the odometer asks your phone to keep the display awake while it runs. In dense cities or tunnels the GPS signal can drop, and the distance for that stretch may be shorter than the real route. On open roads a modern phone is typically within one to two percent of the true distance.

Your car's own odometer counts wheel rotations, so worn or non-standard tyres change its reading. GPS distance is independent of the vehicle, which makes it a useful cross-check. For speed rather than distance, use the GPS speedometer.