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FAQ
Concise, original answers limited to what the tool actually does. No inflated accuracy claims.
What is an online protractor?⌄
An online protractor is a free browser tool that measures angles directly on your screen. You place its center on the vertex where two rays meet, align the rays along the edges, and read the angle live without installing an app.
How do I measure an angle online?⌄
Drag the glowing center to the vertex, align the baseline ray (handle A) to 0° on one edge, drag the second ray (handle B) to the other edge, and read the live interior and reflex values. Use Snap 5° while learning and Off or 1° for fine adjustments.
Can I measure an angle from a photo?⌄
Yes. Click Use image, drag and drop, or paste with Ctrl+V a PNG, JPG/JPEG or WebP up to 12 MB. The file is read locally with FileReader and a blob: URL and never leaves your device. Pan, zoom and rotate the photo, then move the protractor center independently.
Is the online protractor accurate?⌄
The angle math is exact for the points you place. Real accuracy depends on pointer placement, image resolution, perspective, camera lens distortion, transformed or scaled screenshots, browser zoom and line thickness. For safety-critical work, verify with a calibrated physical protractor.
Does it work on phones and tablets?⌄
Yes. The canvas is touch-first with large 28 px hit targets, scrollable toolbar and full-width view optimized for 320–430 px screens. It works with touch, mouse and keyboard and renders useful HTML before JavaScript loads.
Can I measure reflex angles over 180°?⌄
Yes. The tool shows the interior angle up to 180° and the reflex complement 360° minus interior together. Toggle Measure reflex angle to make the larger side primary, or switch to 360° mode for a full-circle view such as 270° or 300°.
What is the difference between degrees and radians?⌄
Degrees and radians are two units for the same angle. 180° equals π radians (about 3.1416), so 90° equals π/2 (about 1.571). Toggle Degrees and Radians in the toolbar — Copy and sharing use the active unit, and precision 0–2 decimals only changes display.
Does the tool upload my image?⌄
No. Images are processed entirely in your browser. They are loaded via FileReader and URL.createObjectURL as a blob: URL, never uploaded to a server. Replacing or clearing the image revokes the URL with URL.revokeObjectURL, and nothing is stored in localStorage or IndexedDB.
Why can a photo angle differ from the real-world angle?⌄
The tool measures the 2D projection you see on screen, not the physical 3D object. A tilted photo turns a rectangle into a trapezoid, a right angle can look acute, and wide-angle lens distortion bends straight lines near the edges. Keep the lens parallel and centered for the closest match.
Can I use it without downloading an app?⌄
Yes. It runs entirely in your browser — no install, no sign-up and no plugins. Open the site on desktop or mobile and measure immediately. You can add it to your home screen for quick access, but it works as a normal web page.