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Why Your iPhone Compass Is Wrong, and How to Fix It

A phone compass is a tiny magnetic field sensor. Most wrong readings come from a magnet or a lump of steel nearby, or from confusing magnetic north with true north. Both are easy to fix once you know.

Updated 1 October 2026

Quick fixes, in order

Take the phone out of any case or wallet with magnets in it, and off any magnetic mount.
Step away from metal: cars, railings, steel desks, laptops and speakers. A metre or two is usually enough.
Calibrate: move the phone slowly through a figure of eight, turning it to face every direction, for ten or fifteen seconds. On iPhone, also check that Settings › Privacy & Security › Location Services › System Services › Compass Calibration is on.
Check which north you are using. On iPhone: Settings › Apps › Compass › Use True North. Turn it on for map work.
Make sure location is allowed for the compass app. True north needs your position to look up the local declination.

How a phone compass works

Inside the phone is a magnetometer, a chip that measures the strength and direction of the magnetic field along three axes. The Earth's field is weak, about 25 to 65 microtesla depending on where you are. A fridge magnet is hundreds of times stronger at close range. The phone combines the magnetometer with its accelerometer, to know which way is down, and its gyroscope, to smooth out movement, and works out which way it is pointing relative to the field.

Anything that adds its own field confuses it. Some things, like a magnet fixed in a case, move with the phone. The phone can learn and subtract those, which is what calibration does. Others, like the steel body of a car or a building, bend the Earth's field itself, and no calibration fixes that. You have to move away from them.

Magnetic north vs true north

The magnetic field does not point exactly at the North Pole. The angle between magnetic north and true north is the magnetic declination (or variation). It depends on where you are and drifts slowly from year to year as the Earth's core changes.

In much of western and central Europe it is small, within a few degrees of zero.
Across the United States it ranges from roughly 15° east in the Pacific Northwest to over 10° west in New England.
Near the magnetic poles it can be tens of degrees, and compasses become unreliable.

A 10° error matters. Over 1 km it puts you about 175 m off your line. Paper maps use true north (grid north, strictly, which is close to it), so for map and compass work, set your phone to true north or add the declination yourself. Official values come from the World Magnetic Model, updated every five years. The current version, WMM2025, runs to the end of 2029. NOAA's calculator gives the value for any place.

Compass heading vs direction of travel

Map apps often show a direction even when the phone is lying flat in a moving car. Once you are moving, many use the GPS course, the direction you are travelling as measured from the satellite positions, instead of the magnetometer, because inside a car the magnetometer is unreliable. Course only exists while you move, though. Standing still, it is meaningless and the app falls back to the magnetic heading. That is why the arrow sometimes swings when you stop.

When to distrust any phone compass

Inside vehicles, trains, lifts and steel-framed buildings.
Close to power lines, transformers, or reinforced concrete.
In high latitudes, near the magnetic poles.
Any time the reading changes as you move the phone a few centimetres sideways without turning it: that is a local disturbance.

For navigation that matters, such as on a boat, in the hills or in the air, carry a proper magnetic compass, and use the phone to cross-check it.

Sources

NOAA NCEI, World Magnetic Model (WMM2025, released 17 December 2024, valid to late 2029), Geomagnetism FAQ (declination; field strength 25,000–65,000 nT) and the declination calculator.
Apple, Use Compass on iPhone, and CLHeading.trueHeading (true north needs location).
Google Maps Help, Find and improve your location's accuracy (figure-8 calibration).