Guides
The file chain from design to printer
- Design: a CAD program saves its own part file, which other tools usually cannot read. Its neutral export is STEP or IGES, exact surfaces with a declared unit.
- Mesh: the part is turned into triangles. STL is the old universal choice; 3MF is the newer one with units and colour; OBJ comes from modelling tools.
- Slice: a slicer cuts the mesh into layers and writes G-code for one specific printer, nozzle and material.
- Print: the printer reads the G-code line by line.
You can join this chain at any step in the browser: STEP to STL, STL to 3MF, the slicer and the G-code viewer.
What file type do 3D printers use: a comparison
| Format | Origin | Units | Colour | Goes into |
|---|---|---|---|---|
| STL | 3D Systems, 1987, for stereolithography | none | none in the standard | the slicer |
| 3MF | 3MF Consortium, founded 2015 | stored, default millimeter | can be stored | the slicer |
| OBJ | Wavefront Technologies, 1980s | none | in a separate .mtl file | the slicer or a modelling tool |
| STEP | ISO 10303, first parts 1994 | length unit stored | colors in AP214 and AP242 | CAD programs |
| G-code | your slicer, for one printer | mm moves | none | the printer |
The short rule is to send a slicer STL or 3MF and keep STEP for anyone who needs to change the design. When the geometry has to change, go back to the model, since G-code only records the moves.
Check the units before you slice
STL, OBJ and PLY store bare numbers. A model drawn in inches and read as millimetres comes in 25.4 times too small, a classic forum complaint. STEP declares its unit, yet some exporters label millimetre values as inches: in the CAX-IF AS1 test assembly that turns a 200 mm part into 5080 mm until you flip the viewer's "Numbers are millimetres" switch. Checking the size before slicing catches both cases in seconds.
Which guide answers which problem
Each guide starts from a question people type into a search box. If a file arrived and you only want to see it, read how to open STL files or how to open a STEP file. Both walk through the viewer and say what to check first. If you need to know what a format can hold before you pick one, the format guides cover what an STL file is, the 3MF file, the OBJ file and the STEP file.
Three guides answer narrower questions. ASCII vs binary STL explains why the same mesh takes 50 bytes per triangle in one form and roughly 280–300 bytes in the other. How to edit STL files covers scaling, cutting and repair in the browser, and says when a sculpting app is the better tool. When a customer wants a price by tonight, how much 3D printing costs breaks it into material weight and machine hours, the same formula the calculator uses.
A reading order for newcomers
Read the STL guide first. Almost every file in 3D printing ends up as a mesh like it, and its missing units explain many of the size mix-ups you will meet. The 3MF guide comes next and shows what the newer format fixes. Read the STEP guide once you work with CAD parts or with suppliers who send them.
Keep the editing and cost guides for the day a real part sits on the bench with a question attached. Each guide links to the tool that does the job, so you can drop your own file on the page while you read, and nothing you open there is uploaded.
Questions and answers
What file format do 3D printers use?
The printer itself runs G-code (or a packaged variant of it). You get G-code by slicing an STL, 3MF or OBJ model for your machine.
Is 3MF better than STL?
3MF is a ZIP package that stores its unit and can store colour and materials, so the size is unambiguous. STL stores neither, yet it remains the format almost every tool accepts. Both slice the same geometry.
Can a 3D printer print a STEP file?
Not directly. A slicer has to turn it into G-code; many slicers want a mesh first, which STEP to STL gives you.
What are 3D printing files called?
Model files (STL, 3MF, OBJ) describe the shape; G-code files describe the moves. People often call both "print files".