Measure from a photo — sizes, distances and radii from one picture
Put something of known size in the photo — a door, a floor tile, an A4 sheet, a folding rule. Mark it, type its size, and every distance, circle, arch or curve on the same surface comes out in cm, m or feet-and-inches, each with an honest ± . Walls and floors photographed at an angle work too. Your photo never leaves your browser. For drawing: set the head (or any length) as your reference with the unit “× reference”, and every measure reads in heads — “figure = 7.6 heads”.
Drop or take a photo with something of known size in it.
Or press Ctrl+V to paste. Images stay in your browser — nothing is uploaded.
Measure walls and floors photographed at an angle
Most photo measuring tools assume you stood exactly square to the wall. Nobody does. This tool calibrates a perspective plane instead: click the four corners of anything rectangular on the surface — a door, a window, a floor tile, a rug, an A4 sheet taped to the wall — and type its width and height. From then on every distance, circle, arch and curve on that same wall or floor is measured on the surface itself, with the foreshortening taken out. A round table top seen at an angle is an ellipse in the photo but a circle on the floor, and the tool gives its true diameter. Click the corners in any order; the tool sorts them, marks which edge is W and which is H, and lets you swap them. For a photo taken straight on, one line of known length is enough.
The calibration is valid for one flat surface. A round table measured against a rug on the floor comes out too big, because the table top is higher. Put the reference on the table top instead (a book, a place mat, an A4 sheet). Points that cannot lie on the calibrated surface — above its horizon — are refused rather than turned into a made-up number, and far-away points get a warning. One surface per photo in this version — measuring areas (m²) comes next.
How to shoot the photo — and which reference to use
- Keep what you measure and the reference on the SAME flat surface — the same wall, the same floor, the same table top.
- Make the reference big: it should fill at least a tenth of the photo; a door beats a light switch.
- Straight-on is best for a single known length; for a wall or floor at an angle, use a rectangle (door, window, tile, rug, A4 sheet) and its 4 corners.
- Step back and zoom in a little rather than going close with the wide lens — ultra-wide (0.5×) lenses bend straight lines near the edges.
- Keep things you measure in the middle of the photo, not at the very edge.
- Measure twice: if the two values differ by more than the ±, reshoot.
| Reference | Size to type |
|---|---|
| Door leaf | 0.90 × 2.00 m (check yours — standard sizes vary by country; in the US e.g. 36 × 80 in) |
| Floor or wall tile | as printed on the box |
| A4 sheet taped to the wall | 21.0 × 29.7 cm |
| US Letter sheet | 8.5 × 11 in |
| Credit or bank card | 8.56 × 5.40 cm (only for small, close-up things) |
| Folding rule or tape laid on the surface | the length you read on it |
Measure your own reference with a tape once — the photo can never be more accurate than the size you type.
What the ± means — honest numbers, not bare ones
Every value comes with a ±, in the same unit as the value: “1.43 m ± 0.03 m”. It shows how far the value can move because points can only be placed so precisely — at the zoom you placed them, with mouse, pen or finger. It covers about 95 % of cases. It does NOT cover things that are not on the calibrated surface, a wrong reference size, or lens distortion. Zooming in when you place points makes the ± smaller, and so does a bigger reference. The tool works it out by re-running the whole measurement a few hundred times with every point nudged by its placement precision; the value itself always comes from exactly the points you set. Circles fitted through more than three points average out the jitter of your clicks, so a round window measured with eight points gets a tighter ± than one measured with three. Units: mm, cm, m, km, in, ft, yd, feet and inches with 1/16″ fractions — and “× reference” for artists, where a head or a hand becomes the unit.
No upload, no account — and you can continue tomorrow
The photo is opened by your own browser and never sent anywhere; there is no server that could see it. Your measures save automatically on this device, together with the image, so tomorrow you open this page, tap the photo under Recent and find the reference, the measures, their names and colors and the ruler exactly where you left them. To move to another device, or to keep your work for sure, save the project file (.json) and open it there. For the boss or the client, share or save the photo as a PNG with every line, name, value and ± drawn in and a legend underneath; for a spreadsheet, export CSV — the Excel DE option uses semicolons and a decimal comma so German Excel opens it correctly. Measuring a screenshot instead of a photo? The pixel ruler works in px, pt, dp and rem, and the color picker reads the colors of the very same image.
Frequently asked questions
Can I measure a wall photographed at an angle?
Yes. Choose “Something rectangular (4 corners)”, click the corners of a door, window, tile, rug or an A4 sheet on that wall and type its width and height. Everything else on the same wall is then measured with the perspective taken out — no need to stand square to it. One surface per photo in this version — measuring areas (m²) comes next.
How accurate is measuring from a photo?
Every value shows its own ±. It covers about 95 % of cases and comes from how precisely the points could be placed — at your zoom, with mouse, pen or finger. It does not cover things off the calibrated surface, a wrong reference size or lens distortion. Zoom in while placing points and use a big reference to make it smaller.
What reference should I use?
Something big, flat and on the same surface as what you measure: a door leaf (about 0.90 × 2.00 m — check yours), a floor tile, an A4 sheet (21.0 × 29.7 cm) or a folding rule laid on the surface. Measure your own reference with a tape once — the photo can never be more accurate than the size you type.
Can I measure a round table or an arch?
Yes. The circle measure takes three or more points on an edge and gives diameter, radius, circumference and area; more points average out your clicks. The arc measure takes start, a point on the arc and end, and gives radius, arc length, chord and rise — for arches, round windows and curved walls. On a perspective plane, a round table top seen as an ellipse still comes out as its true circle.
Why is my measurement too big?
Usually because the object is not on the calibrated surface. The calibration is valid for one flat surface: a round table measured against a rug on the floor comes out too big, because the table top is higher. Put the reference on the table top instead — a book, a place mat, an A4 sheet.
Are my photos uploaded?
No. The photo is decoded and measured entirely in your browser and never leaves your device. Recent images are kept only in your browser’s own storage so you can continue later; you can switch that off or delete them at any time.
How do I open the CSV in German Excel?
Pick the Excel DE option before you export: it separates columns with semicolons and uses a decimal comma, and the file is UTF-8 with a byte-order mark, so umlauts and the ± survive. On German pages it is preselected. “Copy table” pastes straight into Excel, Sheets or Numbers as well.
Can I continue tomorrow or on another device?
Tomorrow, on the same device: yes — the image and its measures are kept in this browser, one tap under Recent brings everything back. On another device: save the project file (.json) and open it there. Safari may clear stored images after about a week without a visit, so save the project file to keep your measures for sure.
Can I use it for drawing proportions (how many heads tall)?
Yes. Mark the head of your figure — or any length you want to count in — as the reference, choose the unit “× reference” and give it a label such as “head”. Every distance then reads in heads (“figure = 7.6 heads”), the ruler is ticked in heads, and each line shows its angle, so you can copy a tilt as well as a length. A drawing-transfer grid and a 3-point angle are coming soon.
How do I draw a straight line?
Hold Shift while you place or drag a point: the line snaps to 45° steps — horizontal, vertical or diagonal — and a small badge shows its angle. Or switch on angle snap (the angle button, or S) for 45° or 15° steps without Shift; Shift then frees the angle. On a surface measured with a reference rectangle the steps follow that rectangle: “horizontal” runs along its width, so a line along a wall seen at an angle still snaps.
Can I measure heights on a photo?
Not yet — measuring off the calibrated surface is planned as an experimental feature. Today you can measure a height that lies on a calibrated wall, for example a window on that wall, but not a person or a lamp standing in the room.