Bubble Level

Plumb level · walls, posts & frames

0.0

Waiting for sensor

0 mm Lean per 2 m 0.0° Sideways tilt
Tap Start to read the sensor

Hold the phone flat against the vertical surface, with the screen facing you and the top edge upward.

How do you check that something is vertical?

Hold the phone flat against the surface. The whole back of the phone should touch it, with the screen facing you and the top edge upward.

Tap Check Plumb. The dashed line represents the surface, and the weight hangs straight down. The gap between them is the lean.

Plumb means vertical. It is the direction a weight on a string points.

Floors and shelves are levelled. Walls, posts and door frames are plumbed. It is the same measurement turned ninety degrees.

How much lean is acceptable?

Building standards use millimetres per storey rather than degrees, because millimetres are what you can check with a straightedge.

Brickwork is usually allowed 3 to 5 mm over a height of 2 m. Door frames need to be closer than this. A frame that is 2 or 3 mm out can make a door swing shut on its own.

If a wall looks straight but reads out of plumb, check what the phone is touching. A camera bump, a lump of plaster or a skirting board will hold the phone away from the surface.

Take readings at three heights and use the number that appears twice.

Frequently asked questions

What is the difference between plumb and level?

Plumb is vertical and level is horizontal. A plumb line follows gravity, and a level surface sits at a right angle to it. Walls and posts are plumbed. Floors and shelves are levelled.

How should I hold the phone?

Flat against the surface with the whole back touching it, the screen facing you and the top edge upward. Remove a case with a raised camera bump, because it is the most common cause of a wrong reading here.

Is a phone as good as a real plumb bob?

For most work it is close enough. A plumb bob cannot lose its calibration, because it is only a weight on a string. A phone can be slightly out without telling you. Use Calibrate to correct it.

What does the sideways tilt figure mean?

It shows how far the phone is rotated within the plane of the wall. It confirms that you are holding the phone square, and it finds a post that is upright in one direction and leaning in the other.

Can I check that something is vertical from a distance?

No. This tool measures the surface the phone is touching. To judge a chimney or a mast from the ground, use a real plumb line or a photograph taken square on.

Does calibrating here affect the other tools?

Yes, and that is intended. Calibrating on this page means that the wall you are holding the phone against is vertical. It saves the same sensor offset the other tools use, so you only need to calibrate once.