Free angle tool

Online Protractor

Measure any angle on your screen: drag the blue arms and read the angle instantly. Free, accurate, and it works on your phone.

Measured angle

60° Acute angle
Reflex
300°
Radians
1.0472
Gradians
66.67
Protractor
Show
Snap
Precision
Units
Image under protractor

Or paste a screenshot with Ctrl+V. The image stays on your device.

Tip: drag the A and B handles onto the two lines of your angle. Drag the center dot or the protractor to move it, and use ↻ to rotate it. Keyboard: Tab to a handle, then use the arrow keys (Shift = 10°).

Calibrate to real size

Hold a credit card, debit card or ID card flat against your screen, lined up with the top-left corner of the blue card below. Move the slider until the outline matches your card exactly. Any standard bank card works: they are all 3.370 × 2.125 inches.

3.370 in × 2.125 in

No card handy? Use your screen size instead

Screen size is less precise than the card method, because it depends on your display scaling setting.

Your calibration is saved in this browser only (localStorage). You'll need to redo it if you change display zoom or scaling.

How to use this online protractor

This free protractor works like the clear plastic one from school, but it is bigger, sharper and gives you the answer as a number. It runs in any modern browser on iPhone, Android, iPad, Chromebook, Windows and Mac.

  1. Put the center on the corner. Drag the dot in the middle of the protractor (or the protractor itself) so it sits exactly on the vertex, the point where the two lines of your angle meet.
  2. Line up arm A with the first line. Drag handle A along one side of the angle. Pull it far out: the longer the arm, the more precise the reading.
  3. Swing arm B onto the second line. Drag handle B until it lies along the other side. Hold Shift or choose a Snap setting to jump in exact steps.
  4. Read the angle. The big number is your angle. Below it you will see the reflex angle (360° minus the angle), the value in radians and gradians, and whether the angle is acute, right, obtuse or reflex.
  5. Fine-tune if you need to. Switch between a 180° and 360° protractor, show 0.1° precision, change units, rotate or lock the protractor, or type an angle like 37 to draw it instantly.

Keyboard friendly: press Tab to focus a handle, then use the arrow keys to move it 1° at a time (Shift + arrow = 10°). The angle is announced to screen readers.

How to measure an angle on your screen, on a photo, or with your phone

Angles on your screen

To measure a diagram, a PDF, a floor plan or a picture you are looking at, take a screenshot (Win+Shift+S on Windows, Cmd+Shift+4 on a Mac) and paste it into this page with Ctrl+V or Cmd+V. The image appears under the protractor and Overlay mode switches to a see-through outline so you can line the arms up with the drawing. You can also click Choose image. Nothing is uploaded.

Angles in a photo

For photos of real objects, like the slope of a roof, the angle of a knee in a squat, or a miter joint, use Measure Angle from Photo. Tap three points (end, corner, end) and it calculates the angle, with a magnifier for pixel-precise placement. You can measure several angles on one image and download the annotated picture.

Angles of real surfaces with your phone

Your phone has a built-in tilt sensor. Lay it on a board, a stair stringer or a table saw blade and the Angle Finder turns it into a digital inclinometer that shows degrees, percent slope and roof pitch. Prefer to aim your camera? The Protractor Camera puts this protractor on top of your live camera view.

Types of angles

Every angle falls into one of six groups. The protractor labels the type for you as you move the arms.

AngleTypeSizeExample
Acute Less than 90° 45°
Right Exactly 90° 90°
Obtuse Between 90° and 180° 135°
Straight Exactly 180° 180°
Reflex Between 180° and 360° 270°
Full Exactly 360° 360°

Want the full picture, including complementary, supplementary and adjacent angles? Read the types of angles guide.

Common angles

See what each angle looks like, how to draw it with or without a protractor, and where it shows up in real life:

Tips for the most accurate reading

  • Go big. Use Fullscreen or drag the Size slider up. Small errors in handle placement matter less on a bigger protractor.
  • Use long arms. Drag each handle as far along its line as you can. The dashed extension lines help you check alignment across the whole screen.
  • Zoom your source, not the protractor. If you measure a pasted image, make it large on the stage before you place the arms.
  • Switch on 0.1° precision when you need decimals, for example in trigonometry homework or when setting a miter saw.
  • Lock it when you are done so an accidental tap does not move the arms.

New to protractors? Our step-by-step guides explain how to use a protractor, how to read the two scales and even how to measure an angle without a protractor.

Frequently asked questions

Is this online protractor accurate?

Yes. The angle is calculated from the exact positions of the two arms, so the math is perfect and the readout goes down to 0.1°. In practice your accuracy depends on how precisely you place the handles: on a phone you can expect about ±0.5°, and on a desktop monitor ±0.2° or better. For the best results, make the protractor large, drag the arm handles far out along the lines you are measuring, and use Fullscreen. That is as good as or better than a typical plastic school protractor, which is marked in whole degrees.

How do I measure an angle on my phone?

There are three ways. To measure an angle that is on your screen (a picture, diagram or PDF), use the protractor on this page. To measure the tilt of a real surface, like a board, a roof or a ramp, lay your phone on it and use the Angle Finder, which reads your phone's motion sensor. To measure an angle on a real object you can see, take a picture and use Measure Angle from Photo, or point your camera at it with the Protractor Camera.

Can I print a protractor?

Yes. The printable protractor page has free 180° and 360° protractors in 4-inch and 6-inch sizes as PDF and PNG files. Print at 100% ("Actual size") and check the 1-inch square on the sheet with a ruler to confirm the scale. Printing on clear transparency film gives you a see-through protractor.

What is a reflex angle?

A reflex angle is larger than 180° but smaller than 360°. Every angle between two arms has a reflex partner that goes the long way around: reflex = 360° − angle. For example, the reflex angle of 60° is 300°. This protractor always shows both values; tap "Reflex" under Show to make the reflex angle the big number.

How do I measure an angle bigger than 180°?

Place the arms on the two lines and choose Show → Reflex. The readout then shows the angle measured the long way around (for example 250° instead of 110°). You can also switch to the 360° protractor to read the full-circle scale directly, or type an angle such as 250 into the "Type an angle" box to draw it.

Does the online protractor work offline?

Yes. After your first visit, the protractor and the other tools are saved by your browser, so they keep working without an internet connection. On a phone you can also use "Add to Home Screen" to open it like an app.

Can I use it to measure a real object at actual size?

Yes. Click "Calibrate screen", hold a credit card against the screen and adjust the slider until the outline matches. Then "Real size" shows a true 6-inch (or 4-inch) protractor, and the arm lengths are shown in inches and centimeters, so you can lay a small object on a tablet or monitor and measure it directly.

Is it free, and do you see my images?

It is 100% free with no sign-up. Everything runs in your browser. Images you put under the protractor, photos and camera frames never leave your device and are never uploaded to a server.

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