How accurate is phone GPS?

What accuracy means

The dot has an uncertainty radius.

GPS.gov gives about 4.9 metres as typical smartphone accuracy under open sky. That describes favourable conditions. It does not mean the phone will always place you within five metres, and it does not turn the displayed coordinate into a surveyed position.

Phone operating systems expose a horizontal accuracy value as a radius in metres around the reported coordinate. It is the system's estimate of uncertainty. It is not a statement that the true position must sit neatly at the centre, or even inside every displayed circle on every update.

Modern phones can combine satellite signals with Wi-Fi, cellular, Bluetooth and device sensors. Apple describes this through Core Location. Android's Location Accuracy service also combines wireless signals and sensors with GPS. The position shown by an app is therefore a phone location estimate, not always a satellite-only result.

The main causes

Weak geometry and reflected signals move the estimate.

• Indoors and undergroundSatellite reception may be unavailable. The phone can fall back to nearby networks and sensors, which may not provide route-level precision.
• Atmospheric conditionsSignal delay through the atmosphere contributes to GPS error, alongside receiver quality and local interference.
• Location permissionIf an app has only approximate location access, the operating system may not supply the precise position needed to compare closely with a route.
• Power settingsBattery-saving modes and restricted location services can limit how often or how accurately the phone updates its position.

Before judging the line

Give the phone a clean chance to locate you.

1. Allow

   Grant precise location access.

   Check the phone's permission for beacen and make sure location services are enabled.

2. Clear

   Move towards a wider view of the sky.

   Step away from a wall, cliff, dense canopy or building when it is safe to do so.

3. Wait

   Let several updates settle.

   A newly opened app or a phone that has moved a long distance may need time to establish a stronger estimate.

4. Compare

   Use more than the dot.

   Match visible paths, contours, junctions and travel direction. Watch whether the marker moves consistently as you walk.

In the field

Separate a GPS problem from a route or map problem.

A mismatch can come from the phone position, the imported GPX line or the underlying map. If the dot jumps while you stand still, the position estimate is suspect. If the dot follows the visible path consistently but the route line stays elsewhere, inspect the route source. If both lines agree but the map feature is displaced, the map data may be the weak link.

Do not make a sharp course change because of one unstable update. Stop somewhere safe, wait for the estimate to settle and compare it with the ground. If confidence does not return, use the established off-route recovery sequence and retreat to the last confirmed point when that is safe.

Position accuracy supports navigation. It does not replace observation or judgement.