Every phone compass — including a browser-based one — reads a magnetometer that senses Earth's magnetic field. That field doesn't point at the geographic North Pole; it points at magnetic north, which sits hundreds of kilometres away and slowly drifts year to year.
The gap: declination
The angular difference between magnetic north and true (geographic) north at any given spot is called declination. It's not a fixed number — it depends entirely on where you are on Earth:
- In parts of the US, declination can be over 15° in either direction.
- In parts of India, it's usually just a few degrees.
- Right on certain lines, it's close to zero.
A simple phone compass, including most free web compasses, shows the raw magnetic heading without correcting for this — which is usually fine for everyday use (finding a rough direction, orienting a map) but matters if you need precision (serious navigation, surveying).
Why the reading drifts or jumps around
Beyond declination, magnetometers are also easily thrown off by:
- Nearby metal — car frames, structural beams, belt buckles, phone cases with magnetic clasps.
- Electronics — speakers, other phones, laptops, wireless chargers.
- Software drift — the sensor's internal calibration can drift over time.
This is why compass apps (and this one) often ask you to wave your phone in a figure-8 motion — it deliberately exposes the magnetometer to a range of orientations, helping it recalibrate its internal offset.
Getting the steadiest reading
- Hold the phone flat and away from your body (pockets, bags with metal, and belt buckles are common culprits).
- Step away from cars, large appliances, and speakers.
- Recalibrate with a figure-8 if the heading seems stuck or inconsistent.
Try it
The free Compass tool reads your phone's magnetometer directly in the browser — no app install, and your readings never leave your device.