STL, 3MF, OBJ or STEP: which file to send, and how to check it first
Four file types reach our inbox. All of them print, but each tells us something different. What they are, which to pick when you have a choice, and a five-minute check that saves a day.
A 3D printer does not print your file. It prints a stack of thin slices that a program called a slicer cuts from your model, and how well that goes depends on what the model tells us. The quote form takes STL, 3MF, OBJ and STEP (or STP) files up to 20 MB. Here is what each one is, which to choose when you have the choice, and what to check before you press upload so the first quote is the final one.
The four formats in one table
| Format | What it holds | Comes from | Our verdict |
|---|---|---|---|
| STL | The surface as triangles. No units, no colour, one object. | Every 3D program; most download sites | Fine. Tell us the size so we can confirm the units. |
| 3MF | Triangles plus units, several objects and settings. | Newer programs and slicers | Best for printing. Nothing to guess. |
| OBJ | Triangles, often with colours and textures. | Art and animation tools, scanners | Fine. Scale is often off; tell us the size. |
| STEP / STP | The exact engineering shape, with units. | CAD programs (Fusion, Onshape, FreeCAD, SolidWorks) | Best for precise parts. We convert it ourselves. |
STL: the universal one
STL is the oldest and most common. It describes the outside of your model as thousands of tiny triangles and nothing else: no units, no colour, no name. That is usually enough. Its one trap is scale: an STL has no idea whether a "1" means a millimetre or an inch, so a model drawn in inches arrives 25 times too small. If you send an STL, tell us roughly how big the part should be, and we check.
3MF: the modern one
3MF was designed to fix STL's gaps. It carries the units, so there is no scale guessing; it can hold several parts in one file, each named; it can store colours; and it compresses well, so the same model is a smaller upload. Almost every program that exports STL today also exports 3MF. If you are given the choice, pick 3MF.
OBJ: from the art side
OBJ comes out of modelling and animation tools and from 3D scanners. Like STL it is a mesh of triangles, but it can also carry colour and texture information, which the printer ignores. OBJ files from art tools are frequently in odd scales or sit far from the origin; nothing we cannot fix, but again, tell us the intended size.
STEP: the engineer's one
STEP (the file ends in .step or .stp) is different in kind. Instead of triangles it stores the exact geometry: a cylinder is a true cylinder, a hole is a true hole with a diameter. Units are built in. For functional parts with fits, threads or precise holes, STEP is the best thing you can send, because we can read a dimension off it or nudge a tolerance without redrawing. We convert it to a mesh for the printer ourselves.
Five checks before you upload
- Units and size. Open the model and read its dimensions. Write the biggest one in the notes field ("about 120 mm long"). This catches the inch problem instantly.
- Wall thickness. Nothing thinner than 1.2 mm; 2 mm is comfortable. A 0.5 mm wall exists on screen and not on the printer.
- Small details. Our nozzle is 0.4 mm wide, so the finest line it can draw is about that. Text should be at least 5 mm tall and raised or sunk at least 0.8 mm to stay readable.
- One solid, or several? If the model is several loose shells touching each other, say so, or send them as separate files. If it is one part with no gaps, you are done.
- Closed surface. A model needs to be "watertight": every edge shared by two faces, no holes in the skin. Most programs have a check or repair command for this. If you are not sure, send it anyway; we run our own repair, and we tell you if the model is beyond it.
Where to get a model if you have none
Ready-made: Printables, MakerWorld, Thingiverse and Thangs hold millions of free models. Send us the link and we download the file ourselves. Make your own: Tinkercad runs in the browser, is free and takes an afternoon to learn; it exports STL and 3MF. For precise parts, Onshape (free for public documents) and FreeCAD export STEP. No model and no time to make one? A photo and a few measurements are enough for most parts.
What we do with your file
We open it, check the scale and the surface, choose the orientation that needs the least support and puts the layers across the stress, and slice it with the settings for the material you picked (or that we recommend). The slicer gives us the weight and the print time, and those give you the price. Your file is used only for your order, it is never shared or printed for anyone else, and it is deleted 30 days after the order is finished; the privacy policy spells that out.
File ready? Drop it in the quote form with the intended size and the material, and the price is on its way on the same working day.
Upload a fileCommon questions
- Which file format is best for 3D printing?
- 3MF, when you have the choice: it stores the units and can hold several parts, so nothing has to be guessed. STEP is best for precise engineering parts because it keeps the exact geometry. STL and OBJ print just as well; just tell us the intended size, since neither records its units.
- What is the difference between STL and 3MF?
- Both describe a model as a mesh of triangles. STL stores only that, with no units, colour or names, so a model drawn in inches can arrive 25 times too small. 3MF adds the units, supports several named objects and colours in one file, and compresses better. Any program that saves STL can usually save 3MF too.
- Can you print a STEP file?
- Yes. STEP (.step or .stp) is the preferred format for functional parts: it holds the exact geometry and units, so we can read dimensions and adjust tolerances without redrawing. We convert it to a mesh for the printer ourselves; you do not need to export an STL.
- How big can the file be?
- The quote form accepts files up to 20 MB. If yours is bigger, do not reduce its quality; email a download link to [email protected] with your name and what the part is, and we treat it like any other quote request.
- What happens to my file after printing?
- It is used only to quote and print your order. We never share it or print it for anyone else, and it is deleted automatically 30 days after the order is finished. We only show a print of your design on our site or Instagram if you say we may.