How to convert SVG to DXF at the right size

You can convert an SVG to DXF for free with Inkscape: turn everything into paths, set the document units to mm, scale to the real size and save as DXF. The thing to watch most is scale — SVG works in pixels at 96 dpi, so 1 px is about 0.2646 mm, and a program that guesses wrong makes the part several times too big or too small. This guide walks through the whole process and how to check the result before it goes to the shop.

Why convert SVG to DXF?

SVG is a vector format made for the web; most logos, icons and patterns you download come as SVG. Laser cutters, CNC routers, plasma tables and factory CAM software mostly want DXF. DXF stores coordinates in workshop units (millimetres or inches) and uses CAD entities — LINE, ARC, CIRCLE — that map straight onto a toolpath. SVG stores pixels, fills, shadows, gradients and nested transforms that a cutter has no use for.

Typical cases: a customer wants a company sign cut from steel or acrylic and only has the marketing team's SVG; a student drew a pattern in Illustrator or Figma and needs to send it to a shop. Both need converting to DXF and checking before they go out.

The scale problem: px is not mm

This is the number-one reason parts come out the wrong size. SVG uses CSS pixels, defined as 96 px per inch. With 1 inch = 25.4 mm:

1 px = 25.4 ÷ 96 ≈ 0.2646 mm, and the other way round 1 mm ≈ 3.7795 px.

To make it worse, some older programs use 72 or 90 dpi (Inkscape before 0.92 used 90), so SVGs from different programs can be off by different amounts. The safe approach is not to trust the scale stored in the file at all: measure after converting and scale to the real size you need. If a sign must be 300 mm wide, scale until the overall width is 300 mm.

An SVG with width="210mm" plus a viewBox already works in millimetres and converts at the right size far more reliably than one that only gives pixels.

Bézier curves and cutting machines

Curves in SVG are Béziers (the C and Q commands in a path), which have no exact counterpart in older DXF versions. A converter can either write them as SPLINE entities or break them into many short straight segments ("flattening"). Splines give small files and smooth curves, but some cutters and CAM programs cannot read them. Flattened curves work everywhere, but too coarse looks faceted and too fine makes huge files and a jerky cutting head.

For general cutting, flattening so the error from the true curve is no more than about 0.05–0.1 mm is enough — less than the kerf of most machines.

Converting SVG to DXF with Inkscape (free)

Inkscape is a free, open-source vector editor for Windows, macOS and Linux with a built-in DXF exporter. Menu names vary slightly between versions; these steps follow Inkscape 1.x.

1. Open the SVG in Inkscape and set the document units to mm in File → Document Properties.
2. Turn everything into paths: select all (Ctrl+A) and use Path → Object to Path. Text becomes outlines and no longer depends on fonts.
3. Turn thick strokes into shapes: if the design was drawn with stroked lines and you want to cut along the outside of the stroke, use Path → Stroke to Path.
4. Remove what the machine does not need: bitmaps, gradients, shadows and hidden objects. Use Path → Union to merge overlapping pieces so no edges are doubled.
5. Set the real size: select everything and type the width in mm in the toolbar, with the aspect ratio locked.
6. Flatten curves if needed: if the target does not accept SPLINE, use Extensions → Modify Path → Flatten Beziers with a suitable tolerance.
7. Save as DXF: File → Save a Copy, type "Desktop Cutting Plotter (AutoCAD DXF R14)". In the options set the base unit to mm and choose LWPOLYLINE output — or pick "AutoCAD DXF R12" if the machine needs the older format.

Check the result in DXCAD2D Online

Do not send a freshly converted file straight to the shop. Check it once; it takes less than five minutes.

1. Open DXCAD2D Online, choose File → Open file… and pick the file from Inkscape.
2. Measure the overall width with a Dimension (D) and object snap (F3). If it is not what you intended, the scale is wrong — go back to Inkscape.
3. Zoom into the curves: they should be smooth, not faceted, and nothing should be missing. (DXCAD2D reads SPLINE, but some shops still do not accept it — if yours asks, flatten Béziers before exporting.)
4. Click each shape with Select (V) and check it is one closed piece, not broken into several.
5. Add fixing holes or adjust distances with Circle (C), Offset (O) and Trim (X) as needed.
6. Export a DXF R12 in mm for the shop, or an SVG to take back into graphics work.

More things to watch

• Details too small to cut: a logo with thin letters or narrow gaps may be impossible to cut in steel once scaled down. As a rule of thumb, gaps and strokes should be no narrower than the sheet thickness.
• Floating islands: letters such as O, A, B, D, P and R have inner pieces that fall out when cut. To keep them, add bridges or use a stencil font.
• Doubled lines from fill plus stroke: some SVGs have a filled shape and an outline exactly on top of each other, which become two sets of identical lines after conversion. Delete one of them.

In short: convert everything to paths, set the units to mm, scale to the real size you need, make the curves readable by the target machine, and measure the result before every send.