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Why is my DXF 25.4 times too big or too small?

Updated Nov 11, 2026

Short answer: The DXF does not say its units, so it was drawn in inches and read as millimeters, or the other way round. Scale by 25.4 and save with units.

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Why it happens

A DXF stores plain numbers, and the unit is a separate setting that many programs leave out. When the unit is missing, the program that opens the file has to guess. Guess wrong and the drawing is off by exactly 25.4 (inches versus millimeters), 10 (centimeters) or 12 (feet).

Drawn inRead asResult
inchesmillimeters25.4 times too small
millimetersinches25.4 times too big
centimetersmillimeters10 times too small

How to fix it

  1. Drop the DXF into the checker above. It shows the size it reads and says whether the file states its units.
  2. If the size is wrong, press "Grow 25.4×" or "Shrink 25.4×", or type the width you meant.
  3. Download the DXF in inches or millimeters. The units are written into the file, so the next program does not have to guess.

Real example: before and after

The example file before fixing, with problems marked: Size may be wrong: 12.0 mm (0.47 in) wide × 4.0 mm (0.16 in) tall
Before, problems marked
The same file after fixing
After

What the checker found

  • Size may be wrong: 12.0 mm (0.47 in) wide × 4.0 mm (0.16 in) tall

What was fixed

  • Grew the drawing 25.4 times (inches that were read as millimeters).

Download: before (DXF) · after (DXF)

Questions

Why exactly 25.4?

There are 25.4 millimeters in an inch. A DXF stores plain numbers. If 4 means 4 inches but the program reads 4 millimeters, everything is 25.4 times too small. The other way round, it is 25.4 times too big.

How do I know which units my DXF uses?

A setting in the file called $INSUNITS says it: 1 means inches, 4 means millimeters, 0 means not saved. The checker reads it and tells you, and warns when it is missing.

Where is the DXF units setting in LightBurn?

Edit › Settings, then File Settings, under DXF import settings. There is also an "Auto-detect units" switch; if a file lies about its units, turning it off and picking the unit yourself helps.

Will the fixed DXF open at the right size everywhere?

The DXF you download states its units (inches or millimeters, your choice), so programs that read the units get it right. If a program ignores units, set its import unit to match.

Sources

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