Bubble Level

How to use the bubble level

1. Open this page on the phone and tap Start level. On iPhone, tap Allow for motion access.
2. Lay the phone flat on the surface. The bubble moves to the high side; when it sits in the small circle and both angles read 0.0°, the surface is level and the ring turns green.
3. To check a shelf edge, door frame or picture, stand the phone on its long or short edge against it. The page switches to the bar level and tells you which side is low.
4. For the best accuracy, calibrate: put the phone on a surface you know is level (or check one by turning the phone round 180° and seeing the same reading), then tap Set zero here.
5. Tap Hold reading to freeze the numbers when you cannot see the screen, such as on a high shelf.

What the results mean

The angle is how far the surface tilts from level, in degrees. As a rule of thumb, 1° is a rise of about 1.7 cm over a metre (or 0.2 inches per foot).

• Under 0.3°: level for any household job: shelves, pictures, a washing machine, a fridge.
• 0.3 to 1°: visibly off over a long shelf or a wide picture frame. Adjust the low side.
• Over 1°: clearly sloping. Liquids in a pan run to one side, balls roll and doors swing.

Phone tilt sensors are accurate to about 0.1 to 0.5° after calibration. A camera bump stops many phones lying flat, so lay it on a book or use a case, and calibrate on the same setup.

The 180 degree check

Not sure the phone itself is accurate? Put it on a surface and note the reading, then turn it round 180° on the same spot. If the surface is level, both readings are 0. If the reading flips sign but keeps the same size (say 0.8° left, then 0.8° right), the surface slopes and the phone is accurate. If the readings differ in size, the phone has an offset: tap Set zero halfway between them, or calibrate on a known level surface. Builders check real spirit levels the same way.

How the phone knows which way is level

The bubble level uses the accelerometer, which always feels gravity pulling down. When the phone lies flat, gravity points straight through the screen; when it tilts, part of gravity shows up on the side axes and the page converts that into an angle. The same sensor runs auto-rotate and step counting. If the level never settles at 0 on a known flat surface, check the sensor with the accelerometer test.

Common problems and fixes

The bubble does not move

Tap Start first, then allow motion access (iPhone). In Chrome on Android, tap the lock icon by the address and allow Motion sensors. A laptop has no tilt sensor.

It never reads zero on a flat table

The camera bump tilts the phone. Put it in a flat case or on a book, then calibrate with Set zero. The calibration is kept on this phone until you clear it.

The reading wobbles

Footsteps, a washing machine or a hand on the table move the phone slightly. Let it settle for a second, or tap Hold reading to freeze it.

Edge mode shows the wrong side

Make sure the screen faces you while the phone stands on its edge. If auto-rotate turned the page, the level follows the screen.