Online protractor
Drag the three points onto the corners of your angle – the angle at the vertex appears instantly. Below, the orientation sensor measures how much the phone is tilted, for example on a roof pitch or ramp.
How it is calculated
Measure an angle on screen
- Drag the dark vertex to the tip of the angle.
- Place the two colored points on the arms.
- The angle between the arms (0° to 180°) appears below, along with the direction of each arm from horizontal.
This lets you measure an angle on a photo or drawing on screen, for example. The angle is calculated from the coordinates with the atan2 function and does not depend on screen size.
Measure tilt with your phone
- Tap “Measure tilt” (on iPhone, confirm the permission).
- Hold the phone on or against the sloping surface.
- Surface tilt: 0° = lying flat, 90° = upright. Long and short edge show the slope of the phone’s edges in degrees and percent.
How it measures
The orientation sensor reports the device’s orientation according to the W3C DeviceOrientation specification. From this the tool calculates the direction of gravity and the angles of the edges. Slope in percent is tan(angle) × 100.
Limits
- On screen, the result depends on how accurately you place the points; photos can be distorted by perspective.
- The sensor is not calibrated; camera bumps and cases can distort the result. For precise work, use a real measuring tool.
Frequently asked questions
How do I measure an angle on screen?
Drag the vertex to the tip of the angle and place the other two points on the arms. The angle appears immediately.
Can I measure an angle on a photo?
Yes, if the photo is visible next to or behind the tool, for example in split screen. Note that perspective distorts angles in photos.
How do I measure a roof pitch with my phone?
Tap “Measure tilt” and lay the phone’s edge on the slope. “Long edge” then shows the angle and the slope in percent.
How accurate is the tilt measurement?
That depends on the sensor and is not guaranteed; cases and camera bumps add error. For precise work, use a proper measuring device.
Is any data stored?
No. Points and sensor values only exist while the page is open and are not sent anywhere.
Sources and legal basis
- W3C – DeviceOrientation Event Specification
- MDN Web Docs – DeviceOrientationEvent
- MDN Web Docs – DeviceOrientationEvent.requestPermission() (iOS)
- MDN Web Docs – Math.atan2()
As of:
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