Bubble level, with degrees

A bubble level (or spirit level) is a tool with a sealed vial of liquid and an air bubble that centers between two marks when a surface is perfectly horizontal or vertical. It tells you whether something is level or plumb, but it doesn’t put a number on how far off it is.

Yes. The Protractor app includes a digital bubble level that uses your iPhone’s accelerometer to show true horizontal and vertical, the same sensor behind Apple’s own level. Unlike a glass vial, it can also show exactly how many degrees off level a surface is.

For hanging shelves, frames, and TVs, checking appliances, and most DIY, a phone level is accurate to within about a degree once it sits flat against the surface. Calibrating it on a known-flat reference first improves the reading. For precision masonry or machine setup, use a calibrated level.

A spirit level shows level with a bubble in a vial — you read it by eye and it only tells you “level or not.” A digital level uses an electronic tilt sensor to show the exact angle as a number, so you can see a surface is, say, 2° off and correct it. A phone app is a digital level you already own.

Yes — the iPhone’s Measure app includes a basic level, because the phone has the accelerometer needed for it. The Protractor app adds a clearer level view plus a live degree readout, percent slope, and an X-in-12 ratio, so it doubles as an inclinometer and angle finder rather than just a level.

Yes. Beyond centering a bubble, the app shows the surface’s exact tilt in degrees — a level with degrees — and can switch the same reading to percent slope or a roof-pitch ratio. That makes it useful for ramps, driveways, and rafters, not only for checking that a shelf is straight.