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How to set the scale on a drawing.
Every measurement from a drawing depends on its scale. If the scale is wrong, every length, area and quantity after it is wrong by the same factor, so set it first and check it.
What a scale means
A scale of 1:100 means 1 unit on the drawing represents 100 of the same unit in real life. So 1 mm on paper is 100 mm on site.
| Scale | Real length of 10 mm on paper | Paper length of 1 m real |
|---|---|---|
| 1:20 | 0.2 m | 50 mm |
| 1:50 | 0.5 m | 20 mm |
| 1:100 | 1 m | 10 mm |
| 1:200 | 2 m | 5 mm |
| 1:500 | 5 m | 2 mm |
Set the scale from a known dimension
- Find a dimension printed on the drawing, such as a grid spacing or a door width.
- Measure that line on screen.
- Enter its real length. The software works out how many screen units are one metre.
- Check the result against a second dimension on the same page.
A 6.0 m grid line measures 1,200 pixels on screen. The scale is 1,200 ÷ 6.0 = 200 pixels per metre. A wall that measures 1,700 pixels is 8.5 m long.
Common pitfalls
- Printed to fit. A drawing printed with "fit to page" no longer matches the scale written on its title block. Trust a measured dimension, not the title block.
- Different scales on one sheet. Details are often drawn at a larger scale than plans. Set the scale again for each view.
- One scale for every page. Pages in the same PDF can have different scales, so set each page on its own.
ISO paper sizes
| Size | Width × height (mm) |
|---|---|
| A0 | 841 × 1189 |
| A1 | 594 × 841 |
| A2 | 420 × 594 |
| A3 | 297 × 420 |
| A4 | 210 × 297 |
An A1 sheet at 1:100 covers 59.4 m × 84.1 m of real ground.
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