Spirit Level
Phone bubble level and inclinometer with calibration and slope percent.
About this tool
Open the page on a phone or tablet and tap Start level; on iPhone and iPad your browser first asks for motion access. In Surface mode, lay the device flat for a round bubble showing tilt in both directions. In Edge mode, stand it on its side against the object you're checking for a tube level with the slope as a percentage. Calibrate sets the current position to zero, and Hold freezes the reading so you can look at it.
How a phone spirit level works
Phones contain an accelerometer that measures acceleration in three directions. When the phone is still, the only acceleration it senses is gravity, so the direction of that force tells you which way is down and how far the phone is tilted. Lying flat, the tilt along the phone's width and length moves the bubble, just as an air bubble rises to the high side of a curved vial in a traditional spirit level. Standing on an edge, the angle between gravity and the phone's edge gives a single reading, shown in degrees and as a slope percentage, where 100% is 45°. Calibration matters, because phone sensors have small offsets and camera bumps or cases tilt the phone. For the best accuracy, place the phone on the surface, calibrate, then turn it round 180° in the same spot: if it doesn't read zero, the true level lies halfway between the two readings. Typical accuracy after calibration is around 0.1 to 0.5°, which is fine for hanging pictures and shelves, levelling a washing machine or a camera tripod, or checking a table. Honest limits: a phone is no substitute for a proper level on building or engineering work, readings jitter if the surface vibrates, and laptops and desktops have no accelerometer. Sensor readings stay on your device. The compass also uses the phone's sensors and the slope calculator converts between angle and gradient.
Frequently asked questions
How accurate is a phone spirit level?
After calibration, typically within 0.1–0.5°, good for shelves, pictures and appliances but not precision building work.
Why does it ask for motion access on iPhone?
Safari on iOS requires permission before a website can read the motion sensors; it's the browser's own prompt.
Does it work on a laptop?
No. Laptops and desktops don't have an accelerometer, so there's nothing to measure.
Is my data saved?
No. Sensor readings are used only on the page and nothing is stored or sent.