Spirit Level (Bubble Level With Your Phone’s Tilt Sensor)
Use your phone or tablet’s tilt sensor to check whether a shelf, desk or floor is level, with a bubble you can read at a glance. It also shows the angle in degrees and the slope in percent. Sensor values are processed only in your browser and are never sent or saved. To measure lengths, try the Screen Ruler.
🔒 Runs in your browser · Your data is never sent to a server
Press "Start sensor". On iPhone and iPad you will be asked to allow access to motion and orientation.
Lay the phone face up on a desk, shelf or floor. When the bubble sits in the center circle, the surface is level.
- Tilt
- -°
- Slope
- -%
- Left-right
- -°
- Front-back
- -°
Zero point (calibration)
If the surface you rest on is not level, you can treat the current position as 0°. Turning the phone around and comparing also reveals any offset in the device itself.
Zero point is set
How to use
- Press "Start sensor". On iPhone and iPad, choose "Allow" in the prompt.
- Pick "Lay flat" (desk or floor) or "Stand upright" (wall or post), then place the phone against the surface.
- When the bubble is centered and "Level" appears, the surface is level. The angle and slope are shown too.
- If the surface itself is tilted and you want it as the reference, press "Set current position as zero".
Notes
- Phone tilt sensors are off by a degree or so depending on the model. For precision work, check with a dedicated spirit level.
- A case or a protruding camera can keep the phone from sitting flush. Rotate the phone 180 degrees and check that the reading flips sign to spot any device offset.
- This does not work on devices without a tilt sensor, such as most PCs, or when motion and orientation access is disabled in the browser or device settings.
- It is easiest to read with auto-rotate turned off and the phone held in portrait.
- Sensor values are only shown on screen, never saved or sent. The zero point also resets when you reload the page.
Glossary
Slope (%)
How much the surface rises per 100 units of horizontal distance: the tangent of the angle times 100. 45° is 100%, and 1° is about 1.7%.
Zero point (calibration)
Registers the current tilt as the reference (0°) and subtracts it from later readings. Use it to cancel an offset that is already in the surface or the device.
FAQ
Does it work on a PC?
Most PCs have no tilt sensor, so no readings arrive and it cannot be used. Try a phone, a tablet, or a 2-in-1 PC with a sensor. On unsupported devices a message explains this.
What if it does not work on my iPhone?
iOS requires you to allow "Motion & Orientation" access when you press "Start sensor". If you declined once, fully quit Safari and reopen the page, or allow it again in the site settings.
It says level, but the surface is slightly tilted.
The phone’s sensor can be off by a bit, and a case or camera bump can stop it sitting flush. Turn the phone 180 degrees and check that the reading flips sign. If the offset is constant, use "Set current position as zero" to correct it.
What is the difference between "Lay flat" and "Stand upright"?
"Lay flat" puts the phone face up and shows the left-right and front-back tilt with a bubble. "Stand upright" holds an edge of the phone against a wall or post and measures only the left-right (in-screen rotation) error, relative to the nearest vertical or horizontal edge.
How do slope (%) and angle (°) differ?
The angle is the tilt itself, and the slope is how much the surface rises per 100 units of horizontal run. Slope is common for drainage and road grades: 45° is 100%, and 1° is about 1.7%.
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