Phone sensors give approximate readings. Don’t rely on them for navigation, construction or anything where safety depends on the result.
Use your phone as a bubble level. Lay it flat for a round level that shows tilt in two directions, or stand it on an edge for a tube level with the angle in degrees and the slope in percent. Readings go to 0.1°, the bubble turns green within 0.3° of level, and you can set zero and hold a reading.
How to use
- Lay the phone flat on a surface for the round bubble level, or stand it on one of its edges against a shelf or frame for the tube level. The view switches by itself; tap Surface or Edge to keep one.
- The big number is the tilt in degrees. On a surface you also see the X and Y tilt; on an edge you see the slope in percent. The bubble turns green and beeps once when it is within 0.3° of level.
- Phone cases and camera bumps tilt the phone a little. Put it on a surface you know is level and tap Set zero, or measure, turn the phone 180° and average the two readings.
- Tap Hold to freeze the reading, for example when you can’t see the screen.
- On iPhone and iPad tap Allow motion sensors first.
- Phone accelerometers usually resolve about 0.1°, but the accuracy you get depends on calibration and the case: expect around ±0.5° without calibration.
- Set zero is saved in this browser for each edge separately. Clear calibration resets it.
- The angle finder measures inclination from horizontal; 90° minus that value is the angle from vertical, also shown on the edge view.
- Sensors are read only on your device. No data leaves the page.
How a phone level works
Phones contain an accelerometer that measures the direction of gravity. When the phone lies flat, gravity points straight through the screen and the level reads 0°; any tilt shifts that direction and the app turns it into angles. Most phones resolve about 0.1°, but cases, camera bumps and factory offsets often add a few tenths of a degree.
To remove that error, put the phone on a surface you know is level and tap Set zero, separately for each edge. Without a reference surface, use the reversal method: take a reading, turn the phone 180° on the same spot and average the two values. Expect about ±0.5° uncalibrated and better after calibration.
Degrees, percent and what they mean
Slope in percent is rise over run × 100, so 1° is about 1.75%, 2° about 3.5% and 45° exactly 100%. For scale: a 1° error across a 2 m shelf is a 3.5 cm drop at the far end, and a 0.3° tolerance is about 1 cm over 2 m. Patios and balconies often slope 1–2% for drainage; many building codes limit wheelchair ramps to 1:12, about 8.3% or 4.8°.
Frequently asked questions
How accurate is a phone bubble level?
Most phones resolve 0.1°. Expect about ±0.5° without calibration because of the case and sensor offset, and roughly ±0.1° to 0.2° after setting zero on a level surface.
How do I calibrate the level?
Place the phone on a surface you know is level and tap Set zero. Or take a reading, turn the phone 180° on the same spot and average the two.
How do I convert degrees to percent slope?
Percent = tan(angle) × 100. 1° is 1.75%, 5° is 8.7%, 10° is 17.6% and 45° is 100%.
Does it work on iPhone?
Yes. On iPhone and iPad tap Allow motion sensors first; Safari asks for permission before a web page can read the sensor.
Can I use it to level a picture frame or shelf?
Yes. Stand the phone on its long edge on top of the shelf or frame. The tube level shows the angle and turns green when it is within 0.3° of level.