A bubble level for your phone, right in the browser
This bubble level turns the motion sensor in your phone or tablet into a spirit level. Lay the phone on a shelf, table or worktop to see a round bubble move towards the high side, or stand it on its edge against a picture frame or a door to use it like a bar level. The exact angle is shown in degrees, as a percentage slope and as the rise in millimetres per metre.
Because phone sensors are rarely perfectly aligned with the phone’s case, you can calibrate to zero on a surface you trust, and lock the reading when you are measuring somewhere you cannot see the screen. It works in Safari on iPhone and iPad and in Chrome, Firefox and Samsung Internet on Android.
Nothing is installed and nothing leaves your device. Desktop computers and most laptops have no motion sensor, so the page tells you if none is found.
How to use the Bubble Level
- Open this page on your phone and press Start level. On iPhone/iPad, tap Allow when asked for motion access.
- Choose Surface and lay the phone screen-up on the surface, or choose Bar and stand it on its long or short edge.
- Adjust the object until the bubble sits in the centre circle and the reading says Level ✓ (within 0.3°). Your phone vibrates once when it gets there, where supported.
- For best accuracy, press Calibrate to zero on a surface you know is level — or use the flip test below.
- Press Lock reading to freeze the numbers, for example when the phone is above eye level.
Bubble Level features
Two modes
Surface mode shows a round bull’s-eye bubble and both tilt directions; bar mode shows a tube level for edges, frames and posts, on any edge of the phone.
Degrees, percent and mm/m
Every angle is also shown as percent slope (tan × 100) and rise per metre, which is how builders and plumbers often specify falls.
Calibrate to zero
Removes the small offset between the sensor and the phone body, plus any camera bump. The calibration is saved in this browser.
Lock reading
Freezes the display so you can read it after taking the phone away.
Rotation-aware
Works in portrait and landscape: readings are converted to the way the screen is currently turned.
Haptic feedback
A short vibration when the surface becomes level, on Android phones that support it.
Degrees, percent slope and millimetres per metre
Percent slope is the rise divided by the run, times 100, which is the tangent of the angle: slope % = tan(angle) × 100. One degree is about 1.75%, or 17.5 mm per metre. Common targets:
| Use | Typical fall | Angle |
|---|---|---|
| Level shelf, table or picture | 0% | 0° |
| Shower floor towards a drain (common guidance) | 1–2.5% | 0.6–1.4° |
| Drain or waste pipe (common guidance) | 1–2.5% | 0.6–1.4° |
| Patio away from a house (common guidance) | 1.25–2% | 0.7–1.1° |
| Wheelchair ramp, maximum (ADA, UK Part M) | 1:12 ≈ 8.3% | 4.8° |
Check and calibrate with the flip test
Lay the phone on a flat surface and note the reading. Turn it 180° on the same spot and read again. If both readings are equal and on opposite sides, the surface itself is tilted by that amount and the phone is accurate. If they differ, the true tilt is the average of the two and the phone has an offset of half the difference.
The quickest fix is to find a position where the readings are the same after flipping — that surface is level — and press Calibrate to zero there. Remove a thick or uneven case first; a protruding camera lens also tilts the phone, so measure on a flat area or calibrate with the same lens contact.
Accuracy and limits
- Phone motion sensors react to very small tilts, but readings can drift by a few tenths of a degree with temperature and case contact. After calibration, expect everyday accuracy of roughly half a degree.
- Use a traditional spirit level for structural work, long spans and anything safety-related; this tool is informational.
- Measure longer surfaces in several places — a phone only rests on a few centimetres.
- For distances, try the online ruler; for directions, the online compass.
Bubble Level FAQ
How accurate is a phone bubble level?
After calibration, usually within a few tenths of a degree on a flat surface, which is fine for shelves, pictures and furniture. Cases, camera bumps and uneven contact add error.
Why does the bubble level say “Lay the phone flat”?
In surface mode the phone must be roughly horizontal. To check an upright edge, such as a picture frame or door, switch to Bar mode.
Does the bubble level work on a laptop?
Only if the device has a motion sensor; most laptops and all desktops do not. Some tablets and 2-in-1 laptops do.
Why does iPhone ask for permission?
Safari requires you to allow motion and orientation access for each site. Tap Start level, then Allow.
What does percent slope mean?
How many units the surface rises per 100 units of length. A 2% slope rises 2 cm over 1 m, which is about 1.15°.
Can I use it to hang a picture straight?
Yes — choose Bar mode, hold the phone’s edge against the top of the frame and adjust until it reads Level.