Turn your phone into a spirit level using the accelerometer, with calibration and readings in degrees, percent and millimetres per metre.
A physical spirit level works because the air bubble inside the liquid rises to the highest point of the curved vial. A phone reaches the same answer by another route: the accelerometer measures the device proper acceleration, and when the device is at rest that reading is exactly the vector pointing at the zenith, with a magnitude near 9.81 m/s². Decomposing that vector along the three device axes gives the tilt from horizontal with tenth-of-a-degree resolution. The tool has three working positions because each one uses a different axis. In surface mode the device lies flat and both screen axes matter, so the bubble is circular and moves in two directions. In wall and edge modes only one axis matters, and the display becomes a tube, like a mason level. The bubble always rises toward the high side, exactly like a real one, so anyone who already knows the physical tool does not have to relearn the sign. The reading appears in three units at once because each trade uses its own. Degrees suit joinery and cutting, percent is what architects and engineers use for ramps and falls, and millimetres per metre is how bricklayers and plumbers talk about floor and pipe slope. They are three ways of writing the same angle.
These references help contextualize formulas, standards, APIs and limitations used on this page. They do not replace professional validation when a result has legal, financial, medical or operational impact.
Once calibrated, a phone accelerometer resolves roughly 0.1 to 0.2 degrees, which is about 2 to 3.5 millimetres per metre. That is enough to set a countertop, hang a shelf, check a washing machine or level a picture frame. It is not enough for precision work such as industrial machine alignment or surveying, where a certified electronic level with arc-second resolution is used.
Tap to turn on the accelerometer. Everything is measured on your device and nothing is sent over the internet.
Lay the device screen up on the surface. The bubble levels both axes at once.
Tip: rest the device on a surface you know is flat and tap Calibrate zero. Without it, the case and the raised camera bump usually cause a fixed error of 0.3 to 1 degree.
Everything is measured on your device. No accelerometer reading leaves the browser, and the calibration is stored only in your phone local storage.