How to scale a PDF in AutoCAD
You import or attach a PDF plan, measure a wall that says 4500 and get 45, or 177, or some number that makes no sense. Nothing is broken. A PDF stores a sheet of paper, so AutoCAD brings it in at the size of the sheet. You fix it once, with one command and one dimension you trust.
Before you start: units and the right dimension
Type UNITS and check the insertion units: millimetres for a metric plan, inches for an imperial one. Then find a dimension on the drawing to scale by. The longer the better, because a small error in where you click matters less on a long line. An overall building dimension is ideal; a door width is a poor choice.
Step by step with SCALE and Reference
If the PDF has vector lines, bring it in with PDFIMPORT; if it is a scan, attach it with PDFATTACH or as an image. Then:
- Type SCALE and select everything that came from the PDF (or the underlay frame).
- Pick a base point, for example one end of your chosen dimension.
- Type R for Reference.
- Pick the two ends of the dimension line on the drawing. AutoCAD now knows its current length.
- Type the real length, for example 12000 for a 12 m wall in a millimetre drawing.
Check it
Run DIST on a second dimension far from the first one, ideally in the other direction. If it also matches the number written on the drawing, the scale is right. If the first matches and the second is off by a few percent, the PDF is probably not square, which is common with scans.
Turn object snaps on when you pick the ends of a vector line; with a scan, zoom in and click the middle of the line's thickness.
When a scan is stretched
A scanner or a phone camera often stretches a page slightly more one way than the other. SCALE changes both directions equally, so it can't fix that. Turn the imported geometry or the image into a block, insert it with different X and Y scale factors worked out from one horizontal and one vertical dimension, and check again with DIST.
If the photo was taken at an angle, the plan is not just stretched but distorted, and no scale factor will fix it. Then it is quicker to redraw the plan than to correct it.
If you only need the plan, not the PDF
Scaling makes the PDF a correct background, but you still have to draw the walls over it. Horezmi does that part: it reads the plan from the PDF, scan or photo and draws it again at real size, with the written dimensions, as a DWG. Check two dimensions with DIST there too before you build anything from it.
Questions
Why is my imported PDF the wrong size in AutoCAD?
A PDF stores a sheet of paper, so it comes in at the size of the sheet. Scale it with SCALE and the Reference option using one known dimension.
Can I scale X and Y differently in AutoCAD?
Not with SCALE. Make the geometry a block and insert it with different X and Y scale factors.
Does PDFIMPORT work on scanned PDFs?
No. A scan has no vector lines to import; attach it as an underlay or image and trace over it, or have it redrawn.