Measuring magnetic field with your phone: steps to test mount hold strength

Part of our guide on magnetic mounts and overheating

Use your phone’s magnetometer to measure magnetic field strength and direction before buying a magnetic mount or wallet.

How to use phone sensors to measure magnetic field strength

Most modern smartphones include a magnetometer sensor designed to measure magnetic field strength typically ranging up to ±50,000 microteslas (µT). To use it, install a reliable magnetometer app that accesses this sensor and displays real-time readings in µT or gauss (1 gauss equals 100 µT).

To measure your magnetic mount’s field, open the app and hold your phone close to the mount or wallet area. Observe the readings as you move the phone around to find where the field peaks. The phone should remain steady while you record the peak value.

Keep in mind the reading depends on distance between the magnet and sensor, phone orientation, and case material. Stronger magnets closer than a few millimeters yield higher readings, while distance rapidly drops the field strength. Testing at typical mount contact distances (1-5 mm) gives the most relevant data.

1. Download and open a magnetometer app using your phone’s sensor
2. Place the phone's sensor side near the magnetic mount or wallet
3. Slowly move phone to find highest magnetic field reading
4. Record the peak µT value and note the phone orientation
5. Repeat measurement at typical use distance with phone case on

Units and typical values for phone magnetometer readings

Phone magnetometers report field strength in microteslas (µT) or sometimes gauss. Residential Earth’s magnetic field ranges 25-65 µT, providing a baseline. Magnetic phone mounts usually create localized fields between 20 and 100 µT near the phone surface, depending on magnet strength and distance. People in this spot often ask about magnet distance and strength effects as well.

Differences in case thickness and materials affect measured values drastically. For example, a metal-backed wallet or case can reduce or distort the field reaching the phone sensor, showing lower or inconsistent readings. Typical strong neodymium magnets in mounts can produce peak fields of 60-100 µT at 1-2 mm distance.

Phone sensor resolution usually spans ±50,000 µT with precision around ±1-5 µT. Values below 20 µT near the phone typically indicate weak or no magnetic mount hold. Keep in mind, sudden spikes or readings near sensor saturation (above 50,000 µT) mean the sensor is overloaded and less reliable.

• Earth magnetic field: 25-65 µT baseline
• Magnetic mount typical field: 20-100 µT at phone surface
• Sensor precision: ±1-5 µT, range ±50,000 µT
• Metal cases reduce or distort readings
• Fields below 20 µT rarely hold phone reliably

How to interpret direction and magnitude for magnetic mounts

Magnetic field direction shown by your phone’s sensor indicates the orientation of the magnetic flux relative to the phone. This direction helps you understand how the mount’s magnetic field lines interact with the phone’s magnetometer and the phone’s internal components. There is more on fix camera not connected after magnetic mount in a separate guide.

When the magnetic field vector aligns well with the phone’s sensor axis, readings are higher and more stable. If the field direction is off-angle, readings drop and the magnetic hold weakens. This means you want to position your mount or wallet so its magnetic poles line up with your phone’s sensor orientation for the best hold.

Magnitude and direction together reveal if your mount applies force symmetrically or pulls at an angle. Uneven pull can cause the phone to slip or cause uneven pressure on the case or wallet, risking damage. Visualizing the 3D magnetic vector from your app helps decide the best placement for your mount.

• Direction shows magnet pole orientation relative to phone
• Alignment with sensor axis increases hold strength
• Off-angle fields weaken magnetic grip consistency
• Uneven pull risks slipping or damage to case and phone

Limitations of phone-based magnetic measurements

Phone magnetometers were designed primarily for compass functions, not precise magnetic testing. They have several limitations that you must consider when using them to evaluate mounts. Sensor saturation from very strong magnets leads to inaccurate or clipped readings, masking real field strength above about ±50,000 µT. There is more on pull force for magsafe ring on squat rack in a separate guide.

Interference from metal phone cases, electronics, and environmental magnetic noise can cause fluctuating or misleading results. Your phone model also affects sensor sensitivity and placement, so readings are not directly comparable between different devices.

The sensor typically measures the field at a fixed internal location which you cannot move. If your mount’s magnet is not near this sensor inside the phone, fields influencing phone holding strength may be missed or underestimated. For best results, combine magnetometer readings with physical hold tests.

• Sensor saturation above ±50,000 µT causes clipped data
• Metal and electronics nearby can distort measurements
• Sensor location inside phone is fixed and unknown
• Readings vary by phone model and case presence
• Physical hold tests remain crucial for final judgment

Steps to measure magnetic field with your phone

To measure the magnetic field strength and orientation of your magnetic mount or wallet, follow these practical steps. This procedure helps you quantify the effective magnetic hold strength and detect potential risk to phone components.

First, download a reliable magnetometer app compatible with your phone. Next, remove any metallic or magnetic accessories from the phone or case to avoid interference. Position the phone so its magnetometer sensor is as close as possible to the mount or wallet magnet, typically on the back center area.

Slowly move the phone around the mount to find the position where the field strength peaks. Record the peak value in µT and note the phone orientation to understand field direction. Repeat this measurement at the actual use distance with your phone case on to simulate real conditions.

1. Install a magnetometer app on your phone
2. Remove metallic accessories and open the app
3. Hold phone sensor near mount or wallet magnet
4. Move phone slowly to find maximum magnetic reading
5. Record peak µT value and note phone orientation
6. Test again with phone case on at typical use distance

What you need to measure magnetic fields accurately with your phone

To get meaningful magnetic field readings from your phone, you need a magnetometer app that accesses the phone’s internal sensor and displays data in microteslas (µT). Many free apps exist, but choose one with clear numeric readout, real-time updates, and preferably visual vector display.

A phone case that does not contain metal or magnets is critical to avoid skewing the measurements. If you want to test the effect of your actual case or wallet, test with and without it for comparison.

Since your phone sensor is fixed inside the device and unknown in position, having a second tool like a dedicated handheld Gauss meter with a probe can verify readings if accuracy is crucial. But for typical gym or car mount choices, a phone magnetometer app usually suffices.

• Magnetometer app showing µT and vector direction
• Non-metallic phone case or case removed for baseline
• Steady hand or stand to keep phone sensor stable
• Optional: handheld Gauss meter for cross-checking

Questions people still ask

I’ve tested magnetic mounts and always measure field strength to avoid surprises with phone hold or damage risk.