Protractor logo Protractor
MEASURE AN ANGLE

Angle measuring tools

Updated — added a short answer to "Can I use my phone as a protractor?"

To measure an angle you need a tool that reads how far two surfaces are turned from each other, in degrees. A protractor does it on paper; an inclinometer does it from level; an angle meter app does it with the tilt sensors already in your iPhone. Here is how the common angle measuring tools compare, and when each one wins.

Angle meter app (phone)

Reads your iPhone’s tilt sensors and shows the angle live — in degrees, percent slope, or ratio. One angle measuring tool for surfaces, slopes, level, and camera angles, always in your pocket.

Protractor

The half-circle scale for measuring an angle on paper or a flat workpiece. Perfect for school and drafting; awkward against a real surface or a corner.

Inclinometer

Measures angle from level — slope, incline, and roof pitch — in degrees, percent, or ratio. Built into the same sensors your phone already has.

Angle finder / gauge

Hinged arms or a magnetic digital gauge for corners, bevels, and saw blades. Compared in detail on the angle finder page.

Can I use my phone as a protractor?

Yes — with a protractor app, your phone does a protractor's job two ways. Rest it on a surface and the Protractor app reads the phone's accelerometer and gyroscope to show that surface's angle in degrees; switch the reading to percent slope or an X-in-12 ratio and it works as an inclinometer. For an angle you can't lay the phone on, the camera protractor lets you point the camera or open a photo, drag two on-screen arms onto the lines and read the angle between them. Sensor readings are accurate to within about a degree for everyday DIY, and the app works offline on iPhone and Android. For an angle on screen or in an image you already have, use the free online protractor; for corners and saw blades, see the angle finder.

Measure an angle with your iPhone

The fastest way to measure a real-world angle is the phone you're already holding. The Protractor app reads your iPhone's accelerometer and gyroscope — the same sensors behind Apple's level — and shows the live angle of whatever surface you rest it on. Lay it on a ramp, a rafter, or a tilted shelf and read the degrees directly. Tap to switch the same measurement to percent slope or an X-in-12 ratio.

For angles you can't lay the phone on, switch to camera mode and align the on-screen arms with the edges. If you'd rather see the step-by-step method first, read how to measure an angle or how to measure an angle with your iPhone. To measure an angle on screen or in an image, use the online protractor.

What an angle meter does

An angle meter is simply an angle measuring tool with a digital readout: a tilt sensor plus a screen. Hardware angle meters cost $20–$60; your phone already contains the sensor, so an angle meter app gives you the same readout for free. The three things a good one does:

  • Zero anywhere. Tap to zero on one surface, rest on the other, and the meter reads the angle between them — a corner, a bevel, a mismatch.
  • Switch units without re-measuring. 26.6° is the same slope as 50% grade and 6-in-12 pitch — one tap converts between them. See degrees, percent, and ratio.
  • Hold a reading. Freeze the number so you can lift the phone off an awkward spot and still read it.

If you need hinged arms or a magnetic gauge for saw setup, that's an angle finder — compared by type, price, and accuracy on its own page.

Which angle measuring tool for which job

FREQUENTLY ASKED QUESTIONS

What tool is used to measure an angle?

The common tools to measure an angle are a protractor (for paper and flat work), an angle finder or sliding bevel (for corners and transfers), an inclinometer (for slope and level), and an angle meter app that reads the iPhone’s tilt sensors. The right one depends on whether you’re measuring on paper, on a surface, or from level.

What is an angle measuring tool?

An angle measuring tool reads the angle between two surfaces or lines and reports it in degrees. It ranges from a printed protractor you read by eye to a digital angle meter or an app that reads a tilt sensor and displays the angle as a number.

What is an angle meter?

An angle meter (or angle measurer) is a digital tool that displays the measured angle as a number rather than a printed scale. A phone running an angle meter app does the same job using the sensors already inside it, with no extra hardware to buy or charge — and can switch the same reading to percent slope or an X-in-12 ratio.

Can I measure an angle with my iPhone?

Yes. The Protractor app uses your iPhone’s built-in accelerometer and gyroscope to measure the angle of any surface you rest the phone on, and a camera mode measures angles you can’t lay the phone against. It reads in degrees, percent slope, or an X-in-12 ratio, and works offline.

How do you measure an angle without a protractor?

Rest your phone flat on the surface and read the tilt the app reports, use the camera mode to align on-screen arms with the angle, or fall back to trigonometry by measuring the two sides and calculating. The phone method is fastest for real-world angles — see our full guide on how to measure an angle.

How accurate is measuring an angle with a phone?

On most iPhones, a sensor-based measurement is accurate to within about a degree once the phone sits flat and still against the surface. Re-zeroing against a known flat reference before you measure improves it further. For certified or machine-shop work, use a calibrated instrument.

4.4
920+ Reviews

Measure any angle,
right from your pocket.

Protractor turns your phone into a precision angle finder, level and inclinometer. Measure anything, anywhere.

Download the App