1
Calibrate the camera
Pick X lines and click both ends of 2–3 straight edges that run in one horizontal direction (floor seams, the long side of a table, a rug). Do the same with Y lines for the direction at right angles.
The yellow horizon and a floor grid appear when the camera is solved. If the grid follows the floor tiles, the calibration is right. Vertical lines are optional, but they let the app double-check — and they are required for level, side-on views.
2
Set the scale
Choose Known size and draw something whose real size you know — a table’s height, a door, a sheet of paper on the floor — then type its size.
A tabletop that overhangs its legs? Use Stacked: floor → top of the leg, then the underside → the top surface at the front edge. A surface at the top is created for you, so you can measure on the tabletop.
3
Measure
Pick Distance, Height, Perpendicular or Area, choose the surface the points lie on, and click.
Rounded corners? Use Corner to intersect two straight edges. Every result shows its 95 % range, a precision badge and what limits it.
Taking a good photo
- Stand at about eye level at a three-quarter angle, with the whole object in frame and some floor around it.
- Use the main lens (1×), not the ultra-wide. Lens distortion is not corrected.
- Don’t crop the photo, and avoid “perspective correction”.
- Include long straight lines in both horizontal directions — tiles, floorboards, a rug, the wall’s base.
- Put your known-size object next to what you measure.
- A tabletop seen from table height is edge-on: its depth can’t be measured. Stand higher.
Reading the results
The value comes from your points; the range is a simulation of small click errors (about ±2 px) and of the uncertainty in your known size.
Precise ±2 % or better · Good ±5 % · Rough wider
A person’s height also depends on posture, footwear and hair. Lens distortion is not corrected. In full calibration the optical centre is assumed to be the image centre.
Keyboard
| V | Select & move points | 123 | X / Y / vertical lines |
| K | Known size | D H S | Distance / Height / Stacked |
| P A | Perpendicular / Area | C | Corner point |
| Enter | Finish stacked / area | Esc | Cancel |
| ←↑→↓ | Nudge point (Shift ×10) | Alt-click | Place without snapping |
| Space-drag | Pan · scroll to zoom | F G | Fit / toggle grid |
| Backspace | Undo the last click | hold Shift | Magnifier while placing |