3D design
STL vs 3MF vs STEP: Which File Should You Send?
Compare STL, 3MF and STEP files for 3D printing and CAD changes. Check units, model versions and source files before requesting design or printing work.
When comparing STL vs 3MF vs STEP, start with the job: are you asking someone to assess a print, change the design or create a model from scratch? STL describes a surface mesh. 3MF can carry a model with additional manufacturing information. STEP is useful for exchanging CAD geometry. The original editable file can be valuable when a design needs substantial changes.
You do not need to convert everything before making an enquiry. Tell us what you have and what you want to change, then agree the files needed for review.
STL: a common surface model for printing
An STL represents the object’s surface using triangles. It is widely used for sharing printable geometry, but it does not preserve a typical CAD modelling history. Editing a hole, wall or curved feature can therefore require a different approach from changing the original design.
STL also does not declare a standard unit of measurement within the file. Include the intended units and at least one known overall dimension. For example, say “millimetres; overall width 120 mm” rather than expecting the recipient to infer the scale. Prusa’s explanation of STL and 3MF describes this limitation.
3MF: model information and potentially a whole project
3MF is designed to hold more information than a basic STL, including units and, depending on how the file is created, colours or manufacturing-related data. A slicer project saved as 3MF may also contain printer, filament and print settings.
That does not make every 3MF ready for another workshop’s printer. Tell the recipient which application created it and whether you intended to share model geometry or a complete slicer project. The recipient should review the setup for their equipment rather than assume those settings are suitable.
Prusa’s current first-print guide notes that opening a 3MF project can bring its own settings. If you are uncertain, keep the original project and ask which export is preferred.
STEP: useful when CAD geometry needs changing
STEP is often useful for exchanging solid or surface geometry between CAD applications. It can be a better starting point than a mesh for work such as adapting an enclosure or changing a feature, depending on the model and receiving software.
A STEP export should not be assumed to include the original feature timeline or all of the author’s design intent. If the work involves ongoing parametric changes, offer the native editable source as well. Agree whether that application and file version are supported before including editable-source delivery in the scope.
Choose by the work you want reviewed
| Your task | Useful starting files | Extra information |
|---|---|---|
| Assess an existing print | STL or 3MF | Units, overall size, quantity and use |
| Modify a designed part | STEP and editable source where available | Required changes and critical interfaces |
| Develop a new idea | Dimensioned sketch, photos and measurements | Purpose, fit and undecided dimensions |
These are enquiry starting points, not a promise that any particular file can be printed or edited without further work. A file extension does not establish printability.
Keep the handover clear
Name the version you want reviewed and identify superseded files. Include a short note explaining the intended use, important dimensions and any mating objects. If the file is scaled, say whether that scale has already been applied.
Share only designs you have permission to share and modify. If you downloaded a model, check its licence and provide the source information relevant to the work. Screenshots can explain the design but do not replace measured dimensions or suitable geometry.
Printer instructions such as G-code are a separate output from the model. They depend on the equipment and setup. For an enquiry, provide the model or brief and let the workshop confirm how it will prepare the print.
Files for a We Glow Up enquiry
STL and 3MF can help us assess printing; STEP or editable source can help with changes. If you have no model, send a dimensioned sketch and several views. We agree formats, revisions and any sample stage before accepting the project.
Use our custom 3D design enquiry page for modelling or changes, or the UK printing enquiry page for an existing model. The brief guide covers measurements, and our UK printing cost guide explains why design work and printing may be quoted separately.