Short answer: hold the phone away from metal and move it in a figure-eight pattern for about ten seconds, rotating your wrist so it passes through all three axes. That is the whole calibration procedure on both Android and iPhone.
Why phone compasses drift
The magnetometer measures the Earth's magnetic field, which is weak â roughly 25 to 65 microtesla. Almost anything electrical or ferrous nearby produces a stronger local field and swamps it.
Common culprits, in rough order of how often they cause the problem:
- Magnetic phone mounts and MagSafe-style accessories â by far the worst offender
- Wireless chargers, even when not actively charging
- Phone cases with magnetic clasps
- Speakers and headphones left resting against the phone
- Car dashboards â a lot of steel and wiring
- Laptop lids, which contain magnets for the sleep sensor
- Reinforced concrete floors and steel-framed buildings
The calibration procedure
It is identical in principle on both platforms: the phone needs to see the field from many orientations so it can work out its own bias.
- Remove the case if it has any magnetic component.
- Step away from metal and electronics â the middle of a room, or outdoors, is ideal.
- Trace a figure-eight in the air with the phone, rotating your wrist as you go so the screen faces different directions through the motion.
- Continue for about ten seconds.
On iPhone: opening the built-in Compass app will prompt you to do this with an on-screen ball-rolling animation when it detects poor calibration.
On Android: there is no dedicated calibration screen on most builds. Open Google Maps and perform the figure-eight; the blue direction cone narrows when calibration succeeds.
How to tell if it worked
Point the phone at something you know the bearing of â a street you can check on a map, or the sun (roughly south at midday in the northern hemisphere, roughly north in the southern). A well-calibrated phone should be within about 5 degrees.
You can check the live reading with our browser compass tool without installing anything â it shows the raw heading and tells you whether the browser is reporting true or magnetic north.
Magnetic north vs true north
These are not the same direction, and the gap matters for navigation:
| Term | What it is |
|---|---|
| Magnetic north | Where the magnetometer physically points. Moves year to year. |
| True north | The geographic North Pole. Fixed. |
| Declination | The angle between them at your location â anywhere from 0° to over 20°. |
Most phone compass apps apply the declination correction automatically using your GPS position, so they display true north. If you are cross-referencing with a paper map, check which north the map uses â most topographic maps are drawn to true north or grid north, not magnetic.
When calibration does not fix it
If the heading is still wrong after calibrating away from all interference:
- Check for a stuck offset. Rotate the phone slowly through a full circle. The reading should change smoothly. If it jumps or sticks, something is still interfering.
- Restart the phone. This reloads the sensor driver and clears a stuck calibration state.
- Try a different app. If two apps disagree, the problem is software. If they agree and both are wrong, it is the sensor.
- Test the raw sensor. A device info app shows live magnetometer values on all three axes. Rotating the phone should produce smooth sinusoidal changes; flat or erratic values indicate a hardware fault.
A note on accuracy expectations
Even perfectly calibrated, a phone compass is a consumer sensor. Within about 5 degrees is realistic and is fine for walking navigation and orienting a map. It is not adequate for surveying, marine navigation, or aligning a satellite dish, all of which need a proper instrument.
