Online Protractor

Measure angles on screen or local photos with draggable rays, paste/drop support, grid and snap controls, radians, placement-sensitivity checks, saved readings, and reusable exports.

Photos stay localupload, drop or paste an image in-browser

Precision controlsgrid, snap, typed angle and 1 px keyboard nudge

Measurement verificationradians, reflex, bearings and pointer sensitivity

Reusable evidencesave readings and export PNG, CSV or audit text

Image angle measurement workspace

Measure the angle, then check how sensitive the reading is to pointer placement

Place a vertex and two rays on the screen or a local photo. Adjust the image, snap or nudge handles, inspect derived angles, save repeat readings, and export an annotated result without uploading the image.

Browser-local · measurement audit

Background imageUpload, drag/drop, or paste an image.Angle displaySnapDecimals Grid overlayGrid spacingImage opacityImage zoomImage rotation °Set included angle °

Drag a handle · tap a handle then use arrow keys for 1 px nudge · Shift+arrow = 10 px

—measured angle

—radians

—angle type

—reflex angle

—complement

—supplement

—ray screen bearings

—ray lengths

—1 px placement sensitivity estimate

Ready.

Saved measurements0 saved

#	Angle	Type	Radians	1 px sensitivity

Accuracy boundary

Pointer sensitivity is not camera accuracy. The estimate uses the current ray lengths to approximate how much a one-pixel endpoint move can change the included angle. Longer rays reduce this screen-placement sensitivity.

Photo perspective, lens distortion, blur, scaling and a misplaced vertex can create larger error. For critical physical measurements, use calibrated equipment and a suitable camera/measurement workflow.

Angle display

Snap while dragging

Precision

Optional background image

The image stays in this browser. Align the vertex and two ray handles to the angle you want to inspect.

Measured angle—

Angle type—

Reflex angle—

Supplement—

Drag the three blue handlesCenter = vertex. The two outer handles define the rays.

Interpretation: screen/photo alignment is a visual estimate. Perspective distortion, lens distortion and imprecise handle placement can change the result; use proper measuring equipment for critical work.

What the browser can measure

Start with a functional check, measure only what the browser can actually expose, then retest after one change.

ConnectChoose the actual browser-visible device or grant permission when required.

TestConfirm basic signal, input, output, preview or display behavior.

MeasureUse browser-exposed levels, timing, resolution, FPS, axes or event data.

DiagnoseCompare the symptom with the specific diagnostic instead of relying on one number.

RetestRepeat after changing the device, cable, permission, browser or system setting.

Pre-call Mic Webcam Keyboard Mouse Gamepad Display Permissions

Browser boundary
These tools observe browser APIs and local media/event streams. They cannot certify hardware condition, bypass denied permissions, or expose measurements the browser/OS does not provide.

Browser-local does not mean laboratory measurement

These pages can report Web API data such as events, stream settings, frame timing and audio samples. They do not certify hardware condition or bypass browser and operating-system limits.

Angle geometry is separated from physical-size calibration

Angle results are scale-invariant browser geometry. Background photos can introduce perspective/lens distortion, and CSS/device-pixel size does not turn the tool into a calibrated physical protractor.