Bubble Level: Digital Spirit Level in Your Browser

A phone estimates orientation from its accelerometer and other motion sensors. Gravity supplies a vertical reference, allowing the browser to report front-to-back pitch and side-to-side roll. The bubble moves away from the centre as either angle grows.

The page uses the same orientation stream as the online compass, but a level does not need magnetic north. A device can therefore support the level even when its magnetometer is missing or unreliable. Browser and hardware support still varies, and sensor access normally requires HTTPS.

This digital reading is useful for quick checks on shelves, tables, pictures, and other household surfaces. It is not a calibrated construction instrument. Use a suitable physical spirit level when tolerances, safety, codes, or paid work require verified measurements.

Side-to-side is the roll angle across the phone's width. Front-to-back is the pitch angle along its length. Zero means the device matches the current horizontal reference after any temporary calibration. Positive and negative signs identify opposite directions; the size of the number shows the amount of tilt.

The page labels a surface level when both axes are within ±0.5°. That threshold is a display choice, not a claim that every phone is accurate to half a degree. Cases, camera bumps, flexible furniture, debris, and a curved phone back can keep the sensor body from sitting parallel to the surface.

For a vertical plumb check, hold a straight edge of the phone against the surface and interpret the relevant axis carefully. A protective case may prevent a clean contact edge. A physical plumb level is safer for work where the result matters structurally.

Select Set current surface as zero to subtract the current pitch and roll from later readings. This compensates for a known reference surface or for the way a particular phone rests. The zero lasts only until the page reloads.

A reversal test exposes systematic error. Note the result, rotate the phone 180° in the same spot, and read it again. A real surface slope reverses relative to the phone; a phone or case offset follows the device. Large disagreement means the setup needs checking.

Remove magnetic accessories only if they affect the device mechanically; the level itself uses gravity rather than magnetic north. Avoid vibration, hold the phone still, and compare more than one orientation. For a compass heading problem, use the separate phone compass calibration guide.