How to scale a PDF drawing to real size
A PDF only knows the size of the paper. To scale a PDF drawing back to real size in CAD you need one dimension you trust: a labelled wall, a door width or the scale bar.
Why is a converted PDF the wrong size?
When a plan at 1:100 is printed to PDF, a 10 metre wall becomes 100 mm of paper. The PDF stores those 100 mm and nothing about the original 1:100. So every PDF to CAD conversion starts at paper size, and the scale has to be set again.
How do you scale it in the converter?
- Drop the PDF into the converter and pick the page.
- Click Set scale.
- Click both ends of a dimension you know. Zoom in with your browser for precise clicks.
- Type its real length, choose the unit (mm, cm, m, in or ft) and press Apply.
- Choose the output units and press Convert to DXF. Every line is now at true size.
Which dimension should you pick?
- The longest dimension on the sheet. A clicking error of 1 mm on a 10 metre wall is far smaller than on a 90 cm door.
- A dimension line, not a wall face. Wall faces carry plaster and line thickness; dimension lines carry the number the designer meant.
- The scale bar when nothing else is labelled. It is drawn to the same scale as the plan by definition.
How do you check the scale afterwards?
In your CAD program, measure a second known dimension far from the first one (DIST in AutoCAD). If both match, the whole drawing is right. A plan printed with "fit to page" has a scale like 1:117 instead of 1:100, which the two-point method handles without any extra steps.
How do you scale it in AutoCAD instead?
Use the SCALE command with the Reference option: select everything, pick a base point, type R, click both ends of the known dimension and type its real length. The result matches what the converter's scale tool does before export.