GUIDE
Calibrating a
PDF drawing.
Measurements are only as good as the calibration behind them. This takes a minute per sheet and saves an argument later.
Why a PDF needs calibrating
A PDF stores geometry in points (1/72 of an inch on paper), not in the metres or feet of the building. A plan printed "at 1:100" on A1 and the same plan printed to fit A3 hold identical drawings at different sizes. Calibration tells the tool how many real-world units one paper unit represents — for that sheet.
Method 1 — enter the drawn scale
If the title block states the scale and the sheet has not been resized, enter it: 1:100, 1:50, 1:200, or an imperial ratio such as 1/4" = 1'-0". Redline offers the common metric and imperial presets and accepts any ratio. This is quickest, and correct when the PDF really is at the printed size.
Method 2 — click a known distance
When the sheet may have been scaled (fit to page, reprinted, scanned), calibrate by measurement: click the two ends of something with a known length — a dimension string, a grid spacing, a door leaf you are sure of — and type the real distance. This is the more reliable method because it does not trust the title block.
Check it
After calibrating, measure a second known dimension somewhere else on the sheet. If it reads right, the sheet is right. If it is off by a constant factor, the sheet was resized: use method 2. If it is off in one direction only, the drawing was stretched and needs a separate X and Y scale.
Every sheet, every time
Calibration belongs to the page, not the file. A drawing set mixes plans at 1:100, details at 1:20 and a site plan at 1:500; measure from an uncalibrated page and the numbers are meaningless. Redline stores the calibration with each page, shows the scale in the status bar, and marks pages that still need it.
Units
Choose the unit you report in — millimetres, metres, feet and inches — once. Everything measured on the sheet is reported in it, whatever the scale, and the CSV export carries it.
Try it on the sample drawing
Redline runs in the browser — nothing to install. Open the demo to try tools on a sample drawing. Demo edits are temporary; your own files, saving, signatures, exporting, printing and downloads come with the seven-day trial, which takes no card. After it you keep Redline Free, or choose Pro at $15 a month or $150 a year. Compare the plans.
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