Photo Room Measurement Tool

Step 1 — Upload a Room Photo

Step 2 — Calibrate with a Known Reference

Click two points on a feature whose real-world size you know (e.g. a standard door is 80–90 cm wide, a brick course is ~75 mm tall, a light switch plate is ~86 mm tall).

Step 3 — Draw Measurement Lines

Click two points to draw each measurement line. Add as many as you need.

Click the first point of a measurement on the photo below.

Step 4 — Export

Download your annotated image or a PDF report with all measurements listed.

How it works

This tool uses a photogrammetric scaling technique: once you establish a ratio between pixels and real-world length, every other distance in the photo can be estimated in the same plane.

Accuracy note: Results are most accurate when (a) the reference feature and the measured feature are in the same physical plane, (b) the camera is roughly perpendicular to that plane, and (c) there is minimal lens distortion. Photos taken at an angle will introduce perspective error.

Frequently asked questions

What kind of reference should I use for calibration?

Use a feature whose dimensions you know with confidence and that lies in the same plane as what you want to measure. Good choices: a standard interior door (typically 80 cm or 90 cm wide, 200 cm tall), a UK light switch plate (86 × 86 mm), a standard brick course with mortar (75 mm tall), an A4 sheet of paper (210 × 297 mm), or a credit card (85.6 × 54 mm). The more pixels your reference spans, the more accurate the calibration — choose something large and clearly defined.

How accurate are the measurements?

Accuracy depends heavily on your photo angle and the calibration reference. For a flat wall photographed straight-on with a good reference, errors of 2–5% are typical. Angled or perspective shots (e.g. a corner room view) will have higher error because a single scale factor cannot account for depth. For critical measurements — structural work, fitted furniture — always verify with a physical tape measure or laser distance meter. This tool is best suited for rough estimates, planning sketches, and insurance or letting documentation.

Is my photo uploaded to a server?

No. This tool runs entirely in your browser using the HTML5 Canvas API. Your photo is loaded into a local canvas element and never leaves your device. There is no server component — the tool works fully offline once the page has loaded. This makes it safe for photos of private homes, commercial premises, or sensitive sites.

Can I measure a floor plan or blueprint instead of a photo?

Yes — the same technique works for any image. Upload a scan of a floor plan, calibrate against a known dimension (e.g. a labelled room width), then measure other parts of the plan. For floor plans you know the scale of, the companion Drawing Scale Calculator may be more convenient.

What is the formula used for the scale and measurements?

After calibration: scale = refRealLength / refPixelDistance (in real-units-per-pixel). For each measurement line: realLength = pixelDistance × scale. Pixel distance is computed as the Euclidean distance between the two clicked points: d = √((x₂−x₁)² + (y₂−y₁)²). Both the calibration reference and each measurement line use the same formula, so the accuracy ratio is proportional to how precisely you click the endpoints.

Can I undo a measurement or re-calibrate?

Yes. Use the delete button (✕) in the measurements table to remove any individual measurement line. To re-calibrate, go back to Step 2 — existing measurements will be recalculated automatically with the new scale. To start over with a new photo, click "Start Over" in Step 4 or refresh the page.