Magnetometer Test
Check your phone's magnetic sensor and measure the magnetic field around you in microtesla (µT). Tap Start, then bring a magnet, a steel tool or a speaker close to the phone: the gauge, X/Y/Z values and live graph react instantly, and a beep sounds when the field rises above your threshold.
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* Heading and dip angle are calculated from the field and are only meaningful with the phone lying flat, screen up.
How to use the Magnetometer Test
- Open the page in Chrome on an Android phone and tap Start magnetometer. If it says the API is missing, enable chrome://flags/#enable-generic-sensor-extra-classes and relaunch Chrome.
- Hold the phone still for a second, away from metal: the tool averages the reading as your baseline (Earth's field, usually 25–65 µT).
- Bring a magnet or metal object close to the phone and watch the total field, the axis bars and the graph rise.
- Set the beep threshold with the slider; the phone beeps faster and higher as the field change grows.
- Sweep slowly over a wall or table to locate hidden screws, studs, pipes or magnets, and tap Set baseline here whenever you move to a new spot.
- Download CSV to keep the raw X, Y, Z and total readings.
What the magnetometer measures
A phone's magnetometer is a tiny three-axis Hall-effect or magnetoresistive sensor. It measures the magnetic flux density along the phone's three axes: X points to the right edge of the screen, Y to the top edge and Z out of the screen towards you. The browser reports each axis in microtesla (µT), and this page combines them into the total field strength:
|B| = √(x² + y² + z²)
Because |B| is the length of the field vector, it does not depend on how the phone is turned. That is why the metal detector compares the total to a baseline: rotating the phone barely changes it, but a nearby magnet or piece of steel does. With the phone lying flat, the page also derives a heading of atan2(−x, y) (the direction the top of the phone points, clockwise from magnetic north) and the dip angle atan2(−z, √(x² + y²)), how steeply the field points into the ground.
Typical magnetic field strengths
| Source | Typical flux density | In gauss |
|---|---|---|
| Earth's field near the equator | about 25–35 µT | 0.25–0.35 G |
| Earth's field in the USA and Europe | about 45–60 µT | 0.45–0.6 G |
| Earth's field near the magnetic poles | up to about 65 µT | 0.65 G |
| Steel screw, nail or tool a few cm away | a change of roughly 2–50 µT | 0.02–0.5 G |
| Fridge magnet held close to the phone | often several hundred µT or more | several G |
| Small neodymium magnet touching the phone | can exceed the sensor's range (often ±1,000–5,000 µT) | 10–50+ G |
Earth's field values follow the World Magnetic Model; exact values depend on your location. Readings close to strong magnets depend heavily on distance, because a magnet's field falls off roughly with the cube of the distance.
Tips for finding metal and magnets
- Find the sensor first: the magnetometer usually sits near the top of the phone. Move a small magnet around the back of the phone and watch where the reading peaks; sweep with that part of the phone.
- Re-set the baseline often: buildings, cars and furniture have their own steel. Tap Set baseline here at each new spot so only local changes trigger the beep.
- Keep the orientation fixed while sweeping a wall for screws or studs; a small calibration offset can otherwise look like a signal.
- Use a low threshold (3–8 µT) to find screws behind drywall, and a higher one (20–50 µT) when you only want strong magnets or speakers.
- Remove magnetic cases and mounts: wallet cases with magnetic clasps and MagSafe-style accessories shift every reading.
- Electrical wiring carrying AC current creates a 50/60 Hz field that is too fast and weak for most phone sensors, so do not rely on this test to locate live wires.
Frequently asked questions
What is a normal magnetometer reading?
Away from metal, a phone should read the Earth's magnetic field: about 25 to 65 µT in total, depending on where you are (roughly 50–55 µT in most of the USA and Europe, lower near the equator, higher near the poles). Values far outside this range with nothing nearby usually mean the sensor needs calibrating, or there is a magnetic case, magnet or steel structure close by.
Why does it say the Magnetometer API is not available?
Web pages can only read raw field strength through the Generic Sensor Magnetometer API, which Chrome on Android offers behind the flag chrome://flags/#enable-generic-sensor-extra-classes. Safari on iPhone, Firefox and desktop browsers do not provide it. Without it, the page can still show a compass heading from orientation events, but not microtesla values.
Can my phone really work as a metal detector?
Only for magnetic (ferrous) metal and magnets at short range. Steel screws, nails, iron pipes, tools and speaker magnets change the field noticeably within a few centimetres. Non-magnetic metals such as gold, silver, copper and aluminium do not affect a magnetometer, so it cannot find them like a real coil-based metal detector.
What is the difference between µT and gauss?
Both measure magnetic flux density. 1 gauss = 100 microtesla (µT), so the Earth's field of about 50 µT equals 0.5 gauss. The tesla is the SI unit; gauss is the older CGS unit still used on many magnets and gauss meters.
How do I calibrate my phone's magnetometer?
Move away from metal and electronics, then slowly wave the phone in a figure-eight pattern several times, rotating it around all axes. Android and iOS use this movement to estimate the sensor's offsets. Afterwards the total field should stay roughly constant while you rotate the phone.
Why does the total change when I rotate the phone?
With a well-calibrated sensor, the total |B| stays almost the same in every orientation; only X, Y and Z swap values. If the total swings by more than a few µT while you rotate the phone in open space, the hard-iron offset is not fully corrected: calibrate with a figure-eight motion, or use the baseline and keep the phone in one orientation while detecting.
Is it safe to hold a magnet near my phone?
Small household magnets are generally harmless to modern phones with flash storage, but strong neodymium magnets can temporarily disturb the compass, magnetic sensors and camera stabilisation until they are recalibrated. Do not hold strong magnets against the phone for long, and keep them away from cards with magnetic stripes.
Are all the tools on FreeToolCabin tested for quality and accuracy?
Yes! Every tool on our site undergoes automated Q/A testing in real browser environments to ensure high precision, correct output, and zero errors. If you happen to spot a bug or have a suggestion, please contact us at [email protected] and our team will review it right away.