Online protractor for angles on screen or photos
An online protractor that combines two measurement paradigms in one tool: a transparent overlay you can drag across the screen like a paper protractor, and a photo-measuring mode where you click three points for an exact angle. Real-world scale calibration via credit card, A4 paper or a coin, simultaneous readouts for supplement, reflex, slope percentage, roof pitch and compass bearing, plus workspace export to PNG, PDF, JSON or CSV — it goes beyond every other online protractor.
How to Use the Online Protractor
Pick a mode: Overlay to measure paper on screen, Image for photos, or Tilt to use your phone
In Image mode — upload, paste (Ctrl+V), drop or capture with camera, then click three points: vertex, first ray end, second ray end
In Overlay mode — drag the protractor, rotate with the green handle, resize with the orange handle, adjust opacity and flip if needed
Read everything at once: angle, supplement, reflex, slope %, roof pitch, bearing — calibrate with a credit card so the on-screen overlay measures and prints at real scale (photo distances stay in pixels)
Save your session as PNG (1×/2×/4×), a PDF report with all angles, a JSON workspace to reopen later, or a CSV for spreadsheets
Measure angles on photos or right through your screen — more modes than any other protractor
Set real-world scale
Place a reference object on your screen, resize the rectangle to match it exactly, then save. This sets the screen scale for the on-screen overlay and 1:1 printing — photo distances stay in pixels.
Place a reference object on your screen, resize the rectangle to match it exactly, then save. This sets the screen scale for the on-screen overlay and 1:1 printing — photo distances stay in pixels.
Export
Features
Frequently Asked Questions
How accurate is the online protractor?
With a desktop mouse practical accuracy is around 0.1°. Snap mode locks you onto exact increments. Calibration does not change angle accuracy — only distance measurements in millimeters.
Why does the protractor on my screen not match a physical one?
Screen pixel density varies by device. Tap Calibrate, pick a reference object (credit card, A4 sheet, or coin) and resize the rectangle to match the real object placed on your monitor. The calibration is stored locally.
Can I measure angles on a photo?
Yes. Switch to Image Measurement mode, upload or paste your photo, then click three points in order — vertex first, then the ends of each ray. Up to 50 angles per session, each with its own color and note.
Does it work on mobile?
Yes. Touch-drag the protractor, pinch to zoom on photos, and use Tilt mode to turn your phone into a physical protractor using its motion sensors. iOS 13+ asks for motion permission once.
Can I print a real-size protractor on paper?
Yes. Calibrate first so the browser knows your screen's pixel density, then use the Print button. It outputs a 1:1 scale page you can cut out and use as a physical protractor.
What is the difference between anchored and 3-point modes?
Anchored mode places a semicircle or full-circle protractor at a fixed point — you rotate it like paper. 3-point mode lets you click any vertex and two ray ends on a photo — useful for irregular shapes like roof lines, physiotherapy joint angles or carpentry.
