Features

Measurement

• Three-point angles. Vertex plus two rays — square vertex handle, hollow ray endpoints, first ray drawn after click 2.
• Chained angles. Click along a path — the first click shows a vertex marker; segments and interior angle arcs update live from the third point; **Enter**, **Finish chain**, or switching tools saves an open chain; click the first point to close and get the angle-sum check (Σ).
• Closed shapes. Trace a polygon and get its interior-angle sum, checked against (n − 2) × 180° with a Σ badge listing which angles are included.
• Lengths. Distance measurements, in pixels or real units once a scale is set.
• Unlimited measurements. in one workspace, all listed together.
• Protractor dial. Classic dual-scale overlay (180° semicircle or 360° circle): drag centre, rotation handle, radius/opacity/colour presets, inner and outer degree scales, align to selected angle; stays centred on the stage when an image is loaded or the view is reset; on narrow viewports the outer scale uses sparse labels (10, 30, 50 …); small dials keep outer numbers tight to the arc.
• Multiple protractors (up to three). Add, duplicate, move, rotate, and show/hide individual dials from floating canvas controls without removing them.

Readouts

• Per-measurement uncertainty. A ± figure from your actual ray lengths and zoom, not a marketing number.
• Inner, outer and reflex. values for every angle.
• Complementary and supplementary. , shown only where they are defined.
• Slope. as a percentage, a 1:n ratio, a roof pitch over 12, and degrees.
• Degrees, radians or gradians. , at 0 to 4 decimal places.

Images and documents

• PDF pages. rendered in the browser, with a page selector for multi-page files.
• PNG, JPG, WebP, GIF and SVG. images.
• Paste a screenshot. with Ctrl/Cmd+V, or drop a file on the page.
• Try an example. — bundled samples (right angle, triangle, roof pitch) load without a file picker.
• Rotate ±90° and flip. horizontal/vertical on the background image before measuring.
• Opacity and lock. for the image layer, so the overlay stays readable.

Precision aids

• Angle snapping. at 1°, 5°, 10°, 15°, 30°, 45° or 90°, with Shift to invert.
• Perpendicular snapping. to an existing ray — for exact right angles to an arbitrary edge.
• Angle guide lines. at chosen degrees, multiple colours, show/hide per guide, clear all.
• Grid overlay. with adjustable spacing (10–200 px presets or custom 5–500 px) and major lines every 2, 5, or 10 cells.
• Ruler overlay. along the top and left edges — **px** until calibrated, then the workspace **Length unit**, with unit suffix on tick labels.
• Grid and ruler toggles. in a compact row above the stage, with **zoom − / + / %**, **Fit/Reset**, and per-dial **Dial 1 / 2 / 3** show/hide toggles.
• Pinch or Ctrl+scroll to zoom. the canvas (up to 40×); plain trackpad scroll moves the page.
• Hand tool. pans the zoomed canvas — tap Hand on mobile and drag with one finger; on desktop use **H**, hold **Space** and drag, or middle-click drag; **Fit** restores the full image when one is loaded.
• Scale calibration. from a known distance, clearly labelled as single-plane.

Keyboard and accessibility

• Every handle is focusable. and nudgeable with the arrow keys — more precise than dragging.
• First-run hints. in a bar above the stage for each tool; dismissed after the first completed measurement.
• Announced values. for screen readers, since the canvas alone conveys nothing.
• Visible focus rings. throughout, and `prefers-reduced-motion` honoured.
• Touch targets of 44px. , and browser zoom is never disabled.
• Mobile-first layout. Measurement results as cards on narrow screens; single-row translucent icon cockpit (Select, Angle, Hand, Chain, Length, undo/redo) that inverts contrast with light/dark theme; zoom and Fit in the bar above the stage; first-run hints above the stage; sparse outer dial labels on narrow viewports; no horizontal page overflow after the first measurement.
• Tool cursors on the stage. Select and Hand use matching pointers; Angle and measure tools use a crosshair centred on the click point; handles keep a pointer for dragging.
• Touch gestures. One-finger scroll passes through the stage to the page (except in Hand mode, where one-finger drag pans); two-finger pinch zooms the canvas; press-and-hold on the protractor dial then drag to move it — pulsing ring while waiting, solid ring when grabbed; scroll lock applies to the stage only while a touch drag is active.
• Touch selection feedback. Selected measurements highlight every handle; the active vertex or ray end gets a link-coloured ring and dashed halo; selected protractor (Select tool) shows rings on the dial, pivot and rotation handle; long-press grab shows pulsing then solid feedback without a permanent ring on load.
• Theme-aware canvas. Default ink measurements and the protractor dial use `--color-ink` so rays and ticks stay visible in dark mode.

Export

• PNG at 1×, 2× and 4×. , rasterised from vector so 4× is genuinely sharp.
• SVG. vector output.
• CSV. with every derived value, Excel-ready (labelled “opens in Excel”).
• JSON. workspace you can re-import.
• Measurement report. — downloadable HTML report with image and table (save as PDF in the browser).
• Print / Save as PDF. through your browser.
• No watermarks. , at any size.

Workspace

• Undo and redo. , where one drag is one undo — and which never disturbs your zoom.
• Autosave and crash recovery. , held locally; compact restore banner.
• Light and dark themes. , following your system by default.
• Erase all local data. in one action.

Learn (site content)

• Tutorials hub. at `/tutorials` — photos, PDF workflow, homework export, calibration.
• How-to-use, accuracy, FAQ, free. pages explain honest limits and verification steps.

Not offered, deliberately

Two things are worth naming, because competitors advertise them:

• Automatic edge detection. On real photographs it is unreliable in ways users cannot diagnose — it silently snaps to the wrong edge and the reading looks fine. Manual placement with a stated uncertainty is more honest.
• Perspective correction. A homography needs four coplanar reference points and then reports confidently wrong lengths for anything off that plane. For a tool that sells accuracy, that is the wrong failure mode.

Open the tool · Why it is free