Accuracy, calibration and troubleshooting

A phone compass is a real instrument, but it is a small one sitting next to a speaker, a battery and a metal frame. Here is what it can and cannot do.

How accurate is a phone compass?

A modern magnetometer in a well-calibrated phone, held away from interference, is typically good to within about 2–5 degrees. That is fine for walking, hiking, finding a landmark, or orienting a tent.

In practice the limiting factor is almost never the sensor — it is the environment. Placed on a car dashboard, next to a laptop, or in a case with a magnetic clasp, the same phone can be off by 20 degrees or more. No app can fix that; it is physics.

±2–5°

Calibrated, clear of interference

±10°

Near a laptop or metal furniture

±20°+

On a car dash or magnetic mount

What interferes with a compass

Magnets — phone cases, car mounts, bag clasps, speakers, headphones. These are the worst offenders by a wide margin.
Large steel objects — cars, railings, bridges, reinforced concrete, boat hulls. Error falls off with distance; a metre or two usually clears it.
Your own body — a phone held against your chest or in a pocket reads differently from one held out at arm's length.
Current draw and heat — heavy charging or a hot phone can add a small, slowly drifting offset.

Troubleshooting

The compass shows a dash instead of a heading

No heading has been measured yet. Until one is, the readout shows -- rather than a number, and a phone that has been sitting idle can take a few seconds to produce its first reading. If no heading ever arrives, the sensor is not being read: on iPhone, motion access has not been granted — tap Enable Compass, and if you already dismissed the prompt, enable Motion & Orientation Access in Safari settings and reload. On Android, make sure the page is loaded over HTTPS. On a laptop without a magnetometer, this is expected: the compass will tell you no sensor was found.

The dial spins or jumps around

That is magnetic interference, not a fault. Move away from metal and magnets, then recalibrate with a figure-8 motion — tap Calibrate under the dial for a guided pass. Screen protectors with magnetic closures and keyboard covers are common culprits.

The heading is consistently wrong by 10–20 degrees

Two likely causes. You may be comparing against true north while the compass shows magnetic north — the compass applies no declination correction, so add your local declination by hand if you need a true bearing. Otherwise the sensor has drifted and needs recalibrating. Try that first, then check the declination.

It worked yesterday and now it is off

Magnetometer calibration drifts over time and after the phone has been near a strong magnet. Recalibrate. It takes about ten seconds.

The compass freezes when I switch apps

Browsers throttle background tabs. Return to the tab and readings resume. This is intentional — it saves battery when you are not looking.

It says no compass sensor found

Your device does not expose a magnetometer to the browser, which is the case on nearly all laptops and some budget tablets. A phone is required for a real heading.

When not to trust a phone compass

Treat this — and any phone compass — as a convenience instrument. Do not rely on it for marine navigation, aviation, surveying, or any situation where a bearing error has safety consequences. For those, use a calibrated magnetic compass and the proper charts, and account for declination and deviation explicitly.

Open the compass How to Use