Online Protractor — Measure Any Angle
Drag the two handles to measure an angle, or add a photo and line the arms up with the angle in the picture.
Drag the two round handles to measure an angle. Drag the center dot to move the protractor.
Drag the center dot onto the corner of the angle, then line up each arm with one side. Your photo stays on your device.
How to use the online protractor
A protractor measures angles in degrees. This one is accurate on any screen: an angle doesn't change when a picture is enlarged or shrunk, so there's nothing to calibrate. Hold an object against the screen or add a photo, then line up both arms with the sides of the angle.
Related guides: How to Use a Protractor
How to use it
- Drag the center dot onto the corner (vertex) of the angle.
- Drag the dark handle along one side of the angle and the blue handle along the other.
- Read the angle below. Switch to 360° for angles over 180°. Arrow keys move a handle 1° (Shift for 10°).
Good to know
- A right angle is 90°, a straight angle 180° and a full turn 360°.
- Acute angles are under 90°, obtuse angles between 90° and 180°, and reflex angles over 180°.
- 180° equals π radians, so one radian is about 57.3°.
- Photos stay on your device; they are never uploaded.
Three ways to calibrate
Auto-detect your device
The ruler recognizes about 130 phones, tablets, laptops and monitors, including iPhones, Galaxy phones, Pixels and MacBooks.
Enter your screen size
Enter your screen's diagonal size (for example, 15.6" for a laptop), and the ruler works out the scale from your screen resolution.
Calibrate with a bank card
Hold any bank card against the outline on screen and move the slider until they match. Bank cards are the same size everywhere: 85.60 × 53.98 mm.
How accurate is the ruler?
How accurate the ruler is depends on how well it knows your screen's pixel density, meaning how many pixels fit in an inch. There are three ways to set it, from most to least accurate:
Bank card (±0.5%): Bank and credit cards are made to one worldwide size, 85.60 × 53.98 mm (ISO/IEC 7810 ID-1). Because every card is exactly the same, matching one on screen gives the most accurate result.
Auto-detect (±1%): The ruler looks up your device's published screen size and resolution. Screens of the same model can differ very slightly, so this is a little less exact. It covers about 130 devices.
Screen size (±2%): You type in your screen size, and the ruler works out the rest from your resolution. Advertised sizes are rounded (a "15.6-inch" screen may really be 15.59 inches), so this is the least exact method. It's a good fallback when you don't have a card.
Real-life objects to check your measurements
Use these everyday objects to confirm the ruler is calibrated correctly.
Bank or credit card: 85.60 × 53.98 mm (3.37 × 2.13 in)
A4 paper: 210 × 297 mm (8.27 × 11.69 in)
US Letter paper: 8.5 × 11 in (215.9 × 279.4 mm)
US quarter: 24.26 mm (0.955 in) across
1 euro coin: 23.25 mm (0.915 in) across
AA battery: about 50.5 mm long and 14.5 mm wide