How to set scale on a scanned plan
Quick answer
Scanned or photographed plans have no reliable paper size, so scale presets can't be trusted. Instead, draw a line over a dimension you know the real length of (a stated dimension, grid spacing or scale bar) and enter that length — the tool calculates the scale from it.
Ratio presets like 1:100 only work when the PDF is at its true paper size. A scan, a photo of a drawing, or a PDF that's been resized loses that guarantee — so measuring against a preset gives wrong numbers.
The fix is calibration: tell the tool one real-world distance and let it work out the rest. Here's how to do it accurately.
Step by step
- 1
Find a known dimension on the drawing
Look for a stated dimension line, a structural grid spacing, a door width, or a printed scale bar — anything where you know (or can read) the real length. The longer and clearer, the more accurate your scale.
- 2
Choose "draw a known dimension"
In the set-scale dialog, choose to draw a known dimension (calibrate) rather than a preset ratio.
- 3
Draw along that dimension
Click one end and then the other end of the known distance, as precisely as you can. Zoom in first — a few pixels of error at high zoom is far less than at fit-to-screen.
- 4
Enter the real length and units
Type the true length (e.g. 5.4) and pick the unit (m, mm, ft…). The tool converts your pixel measurement into a real-world scale for that page.
- 5
Verify against a second dimension
Measure a different known dimension and check it reads correctly. If it's off, recalibrate using a longer reference line.
- 6
Measure as normal
With the scale set, run your linear, area and count take-off — every measurement on the page is now in real units.
Tips & gotchas
- •Calibrate off the longest known dimension you can find — it minimises error.
- •Scale is per page: multi-sheet PDFs at different scales need calibrating per sheet.
- •Photos taken at an angle are distorted and won't measure true — use a straight-on scan where possible.
- •If the scan is skewed, calibrate along the same axis you'll mostly measure in.
Frequently asked questions
Why don't scale presets work on a scanned plan?
Presets assume the PDF is at its true paper size, so one PDF point equals a known real distance. A scan or resized PDF breaks that assumption, so presets give inaccurate measurements. Calibrating from a known dimension avoids the problem.
What if there's no dimension on the drawing?
Use any element whose real size you know — a standard door leaf (often ~0.9 m), a grid spacing, or a printed scale bar. Accuracy improves with longer references.
Do I have to set the scale on every page?
Yes if pages are at different scales. Scale is stored per page, so calibrate each sheet you measure.
Can I do this for free?
Yes — draw-to-calibrate is included on Solid Takeoff's free plan.
Try it on your own plan — free
Open a PDF and measure in your browser. No card, no install, no CAD. Free plan forever.