Help · Measure tool
How to Measure Distances on an Image Online
Once your image is calibrated, the measure tool turns every line you draw into a real-world distance. It is the fastest way to measure a room on a floor plan, a wall in a photo or a plot on a satellite image — without CAD software and without uploading your files to a server.
Draw your first measurement
Select the Measure tool (pencil-ruler icon, or press L) and click the start point, then the end point. You can also click and drag in one movement and release at the end point. The length appears above the line in the unit you used for calibration, and it is added to the Measures list in the sidebar.
While you draw, a small badge next to the cursor shows the line angle in degrees (0° points right, 90° points up). Press Esc to cancel a line after placing the first point.
Keep lines straight: angle constraints
Hold Cmd (Ctrl on Windows) to lock the line to 0° or 90° — perfect for walls, doors and dimension lines. Hold Alt to snap the line to 45° steps for diagonals and chamfers. The angle badge turns orange whenever a constraint is active.
Hold Alt + Cmd together to freeze the current angle: from that moment only the length changes, so you can extend a measurement along an inclined wall or roof edge without drifting. The same shortcuts work when you drag the end handle of an existing line.
Every line shows its midpoint as a small diamond. When you draw or drag a point near the midpoint or the end of another line, it snaps to it (and anywhere along other lines or circle outlines) and a ring highlights the target — handy to measure from the centre of a wall or to chain measurements. Hold Shift to turn snapping off when you need to place a point very close to them.
Edit, rename and lock measurements
Switch to the Pan (H) or Select (A) tool and click a line or its label to select it. Drag the round handles at each end to adjust a point, or drag the label to move the whole line. Double-click the label to give the measurement a name such as “Kitchen width”.
When a measurement is final, click the small padlock that appears under the selected line, or press K. Locked lines cannot be moved by accident while you keep working on the plan. Click the padlock again to unlock it. Delete a measurement from the list in the sidebar; Cmd/Ctrl + Z undoes any change.
How accurate is measuring on an image?
Accuracy depends on the calibration reference, the image resolution and perspective. On a scaled floor plan or blueprint, results are usually within a few centimetres. On photos, measure only objects that are in the same plane as the reference and confirm critical sizes on site.
Zoom in before placing points to click exactly on edges. If you measure the same distance twice and get different results, check the calibration line first — every measurement depends on it.