How to measure a PDF floor plan online, free
You have a floor plan as a PDF — from an architect, an estate agent, or a planning portal — and you need real dimensions off it: a wall length, a room size, whether the sofa fits. Here's how to do it in your browser, in about a minute, without printing anything.
Why you can't just trust the stated scale
Most plans say something like 1:100 or 1/4″ = 1′-0″ in the title block. That ratio was true on the original sheet of paper — but a PDF gets exported at arbitrary page sizes, viewed at arbitrary zoom levels, and often passed through an email or a portal that resizes it. On your screen, the stated scale is broken. (If you're curious how drawing scales work, see our guide to architectural scales.)
The reliable approach is calibration: instead of trusting the label, you tell the tool the real length of one thing on the drawing, and it works out the true pixels-per-metre from that. Every other measurement follows.
Step by step
- Open Scale Rule and drop the PDF in. Go to the app — there's no account or install. Drag the PDF onto the upload box (up to 30 MB). Each page renders right in your browser; a multi-page PDF becomes a multi-page drawing. Nothing is uploaded to a server.
- Find a known dimension. The best candidates, in order: a printed dimension line (e.g. a wall labelled 4200), a scale bar, or a feature with a standard size — a door leaf is typically 762–838 mm (30–33 in) in UK/US homes.
- Calibrate. Choose Set scale, click each end of the known dimension, and type its real length — Scale Rule accepts 4.2m, 420cm, or 13ft 9in. That one line sets the scale for the whole page.
- Measure. Use the distance tool for wall-to-wall lengths, the path tool for anything with corners (skirting, pipe runs), the area tool for rooms, and the angle tool for corners that don't look square. Values update live as you drag; switch metric/imperial any time.
- Sanity-check and export. Measure a second labelled dimension and check the tool agrees with the label — that validates your calibration. Then copy values individually, or export the whole list as TSV or Markdown.
Accuracy tip: calibrate against the longest known dimension you can find. A 1-pixel click error on a 60-pixel door is nearly 2%; the same error on a 600-pixel building width is 0.2%. Adding a second calibration line averages out click error further — Scale Rule warns you if your calibrations disagree by more than a few percent.
Common problems
"Do not scale" is written on the drawing
Standard practice on construction drawings — it means dimensions printed on the drawing take precedence over anything you measure, because the geometry may not be perfectly to scale. Measured values are still fine for estimation, but treat printed dimensions as the truth wherever they exist, and verify on site before committing money.
The PDF is a scan or a photo
Scanned plans work as long as the page was flat and square to the scanner. Photos of paper plans introduce perspective distortion — see our guide to measuring from a photo for how to shoot one that measures well.
No dimensions anywhere on the plan
Calibrate against a standard-size feature (door ≈ 762–838 mm, bath ≈ 1700 mm, single bed ≈ 1900 mm) and treat everything as an estimate — good enough for furniture planning, not for ordering materials.
FAQ
Can I measure a PDF floor plan without printing it?
Yes. A browser tool like Scale Rule renders the PDF on screen and lets you calibrate against one known dimension, after which every measurement you draw reads out in real units. No printing, no ruler, no PDF editor needed.
The plan says 1:100 — why can't I just use that scale?
A stated scale like 1:100 is only true at the drawing's original paper size. The moment a PDF is exported, resized, or viewed on a screen, centimetres on your display no longer map to the stated ratio. Calibrating against a known dimension inside the drawing sidesteps this entirely and works at any zoom.
What if the floor plan has no dimensions written on it?
Calibrate against something with a standard size: an interior door leaf is commonly about 762–838 mm (30–33 in) in UK/US homes, a bath is about 1700 mm long, a single bed 1900 mm. These give a usable estimate — treat results as approximate and verify on site for anything that matters.
Ready to try it on your plan? Free, no sign-up — and the PDF never leaves your device.
Open Scale RuleMore guides
- Architectural scales explained 1:50, 1:100, 1:200 and their imperial equivalents — and why calibration beats all of them on screen.
- How to measure area on a plan Room areas, gardens and plots — trace a polygon, read m² or ft².
- Measuring from a photo of a plan When a phone photo is good enough, and how to shoot one that measures well.