Bubble Level

What is a bubble level?

A bubble level – also called a spirit level – is a tool for checking whether a surface is level (perfectly horizontal) or plumb (perfectly vertical). The classic version is a sealed vial of liquid with one trapped air bubble: when the bubble sits exactly between the two marked lines, the surface underneath is level. This page is a bubble level tool that runs entirely in your browser.

How to use this bubble level?

Getting a reading takes three steps: Tap “Start Measuring.” On an iPhone, Safari will ask for permission to use motion sensors the first time – tap Allow. This is a standard iOS privacy prompt, not something specific to this site. Set your phone down on the surface you’re checking, or hold it flat against a wall or a straight edge for a plumb check. Let it sit still for a second so the reading can settle.

How to read a bubble level?

This tool shows two views, and switches between them automatically depending on how you’re holding the phone. Lay the phone flat and you get a bullseye: a small dot inside a ring, exactly like a builder’s circular bubble level, with degrees for both the left-right and front-back tilt.

How does a bubble level work?

A physical spirit level uses simple physics: the bubble is lighter than the surrounding liquid, so it always floats to the highest point of the curved tube. A phone-based digital level measures the same underlying thing – which way gravity is pulling – electronically, through the accelerometer built into every modern smartphone.