Laser file imports at the wrong size
The design should be 100 mm wide, and your laser software says 377.95 mm, or 3.94 mm, or 133.33 mm. The good news: the exact ratio tells you what went wrong.
Short answer: divide the size you get by the size you expected, then look up the ratio below. Almost every case is a unit mix-up between millimetres, inches and pixels.
Find your ratio
| Size you get ÷ size you expect | What happened | Example (100 mm design) |
|---|---|---|
| 25.4 | Inches read as millimetres | 2540 mm |
| 0.0394 (1 ÷ 25.4) | Millimetres read as inches | 3.94 mm |
| 3.78 | Pixels read as millimetres (96 px per inch) | 377.95 mm |
| 0.265 (1 ÷ 3.78) | Millimetres read as pixels | 26.46 mm |
| 1.333 | File made at 72 px per inch, read at 96 | 133.33 mm |
| 0.75 | File made at 96 px per inch, read at 72 | 75 mm |
| 1.067 | File made at 90 px per inch (old Inkscape), read at 96 | 106.67 mm |
If your ratio is none of these, the design itself was probably scaled, or the size includes something you did not expect (a page frame, a hidden object, a stroke width).
Why units get lost
In SVG files
An SVG can give its size in real units (width="100mm") or in pixels, or not at all. Pixels have no physical size: a program has to assume a resolution. Most current software assumes 96 pixels per inch, but older Illustrator files assume 72 and Inkscape before version 0.92 used 90. Two programs that assume different values give two different sizes for the same file.
In DXF files
A DXF stores plain numbers. The unit is an optional setting in the file header. When it is missing, your laser software guesses, usually millimetres, sometimes inches, depending on its settings.
How to fix it
- Quick fix: in your laser software, scale the design by the inverse ratio (for example 1 ÷ 25.4 = 3.937 %), using the number box rather than dragging. Fine for a one-off, but easy to forget next time.
- In your design software: set the document unit to millimetres and the page size in millimetres before exporting. In Inkscape, see File → Document Properties. In Illustrator's DXF export options, set the scale to 1 mm = 1 unit.
- In LightBurn: check the DXF import unit settings in Edit → Settings (unit detection and the fallback unit). See importing into LightBurn.
Or convert with the unit written in
Our converter reads the SVG's real size (mm, cm, in, pt or px at 96 per inch), shows you the final size in millimetres before you download, and writes millimetres into the DXF. When the SVG only gives pixels, it says so, so you can check.
Convert an SVG to DXFCheck before you cut
- Select everything and read the width and height in your laser software.
- Compare with one dimension you know for sure (a hole for a 3 mm screw, a 100 mm panel).
- If a test piece is cheap, cut a small square with a known size first.
Questions
Why is my DXF 25.4 times too big?
The drawing was made in inches and read as millimetres (1 inch = 25.4 mm). Set the import unit to inches, or convert with a tool that writes the unit into the DXF.
Why is my SVG 3.78 times too big?
Pixel values were read as millimetres. At 96 pixels per inch, one pixel is 0.2646 mm, so a value read as millimetres comes out 3.78 times too large.
What does a 1.33 ratio mean?
One program used 72 pixels per inch and the other 96. 96 / 72 = 1.333. Older Illustrator files and some exporters use 72.