STL vs 3MF (and OBJ, STEP): Which File to Send
What each format carries, the units mistake that shrinks a part 25 times, and exactly what happens when you upload one.
Use 3MF when you can, STL when you must. Both carry the shape, which is all a printer needs. The difference is what else travels with it. An STL is a bare list of triangles with no units, so the software at the other end has to guess whether you drew it in millimetres or inches. A 3MF knows its units and can hold several parts in one file. Where your model comes from decides which one to send.
Where does the model come from?
What is it?
Send
3MF, or STEP
From CAD, a 3MF keeps the units and the exact geometry. A STEP file works too: we convert it to a mesh on our slicer before measuring it.
Upload it and see the price- STL
- Triangles only. No units, no colour. Universal.
- 3MF
- Triangles plus units, parts and colours, zipped. The modern default.
- OBJ
- Triangles, sometimes with a separate colour file. Common from 3D art tools.
- STEP
- Exact CAD surfaces, not triangles. We convert it to a mesh to slice it.
We accept all four. Longest side up to 255 mm; uploads up to 500 MB, the instant quote up to 25 MB.
The mistake that costs the most
An STL drawn in inches arrives 25.4 times too small, because an STL has no units at all.
How to catch itLook at the measured size after uploading. A phone stand that reads 3.5 mm wide was drawn in inches.
The four formats, plainly
- STL
- The oldest and most universal. A surface made of triangles, nothing else: no units, no colour, no parts. Every slicer and every model site uses it.
- 3MF
- A newer, zipped package. It holds the mesh with its units, can keep several parts and colours, and can carry print settings. Most modern slicers save it by default.
- OBJ
- A mesh format from 3D graphics. It can point to a colour and texture file beside it. Common from sculpting and scanning tools.
- STEP
- An engineering format that stores exact curved surfaces rather than triangles. Ideal for passing designs between CAD programs; a slicer converts it to a mesh first.
What happens when you upload one to us
- All four are accepted
- STL, 3MF, OBJ and STEP. We check the contents, not just the extension, so a renamed file is refused.
- STEP and OBJ are meshed
- Converted to a mesh on our slicer, then measured like any other upload.
- Sliced for a real price
- Every design is sliced on our production profile: weight in grams, print time and size in millimetres, and the price comes from those.
- One colour per design
- You pick the plastic and the colour when you order. Colours or settings saved inside a 3MF are not used, so split a two-colour product into parts.
- Size limits
- Up to 255 mm on the longest side and at least 0.5 mm on the smallest. Files up to 500 MB, or 25 MB for the instant quote.
We do not repair meshes beyond flipping faces that point inwards, so a model with holes or overlapping shells is sliced as it is. Most models from CAD and from model sites are already clean. If you do not have a file at all, start with how to get something 3D printed, and before selling a downloaded model, check whether its licence allows it.
FAQ
For most uses, yes. A 3MF stores its units and can hold several parts, colours and print settings; an STL is only a mesh with no units. STL is still universal and prints just as well when its size is right.
An STL has no units, so software assumes millimetres. A model drawn in inches arrives 25.4 times too small, and one drawn in centimetres arrives 10 times too small. Export in millimetres, or use 3MF.
Yes. A STEP file is converted to a mesh before slicing. We accept STEP uploads directly and convert them on our slicer.
Not with us. Each design is printed in the one material and colour you choose when ordering. For a multi-colour product, export each colour as its own part.
Any of the four. A price in seconds.
Upload an STL, 3MF, OBJ or STEP file and we slice it on the spot: the measured size, the grams, the print time and a price per part, no account needed.
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