Updated 2026-09-05 · 6 min read
STL vs 3MF: which file should you send?
Quick answer
STL is the oldest and simplest 3D file. It only holds the shape, not the real size or the color. 3MF is newer. It can hold the shape, the real size, and the color together in one file. We print from both. If your file came straight out of a slicer like Bambu Studio, PrusaSlicer, or Cura, send the 3MF. If a model page only offers one file, send whatever it gives you.
Upload your file and get one printed for you.
You found a model online and it comes with a file ending in .stl or .3mf, or both. Both work here, but they are not the same thing, and knowing the difference helps you pick the one that prints closest to what you expect.
What STL actually is
STL is an old format, from the 1980s. It only describes a shape: a pile of tiny triangles that make up the surface of your model. That is all it knows how to say.
It has no idea what unit it is in. A cube saved as "10" could mean 10 millimeters or 10 inches, and the file itself never says which. It also has no idea about color, and it can only hold one shape per file.
What 3MF adds
3MF is a newer format built for how people actually use 3D printers today. A 3MF file can carry the shape, the real world size in a stated unit, the color or material a designer picked, and more than one part placed on a plate, all in one file.
That is why a file straight out of a slicer, like Bambu Studio, PrusaSlicer, or Orca, is usually a 3MF: the slicer is set up to save all of that at once.
STL and 3MF side by side
| What it does | STL | 3MF |
|---|---|---|
| How old it is | A simple format from the 1980s | A newer format built for modern 3D printers |
| Stores the real size | No, it is just numbers with no unit attached | Yes, it states its own unit |
| Can hold more than one part | No, one STL is one shape | Yes, several placed parts in one file |
| Can hold color | No | Yes, though we print every order in one color |
| Works with our upload tool | Yes | Yes |
What each format can and cannot hold, and whether we print it.
Why an STL sometimes prints the wrong size
Because STL carries no unit, a file saved in inches can look 25 times too small once a tool reads it as millimeters, or the other way around. This is the single most common reason a print comes out the wrong size. See our guide on checking an STL's dimensions for how to catch this before you order.
Our upload tool watches for a suspiciously tiny model and asks you to confirm the unit before it prices the file. 3MF avoids this problem entirely, because the unit rides along with the shape.
Worth knowing
What to know before you send either one
We print every order in one color, even if a 3MF was set up with several colors in a slicer. A very detailed 3MF can take our system a little longer to read than a plain STL. And a file with holes or broken geometry will not print no matter which format it is in. Fix that in your modeling program first, or upload it and ask us to take a look.
- Can I send a STEP or OBJ file instead?
- Not yet. Our upload tool reads STL and 3MF files. If your model is a STEP or OBJ file, export it as an STL or 3MF from your design program first, or ask us for help.
- Which file is smaller?
- STL is usually smaller for one simple part. 3MF can be bigger, because it can carry extra data like color and multiple parts.
- Do I need to know which one to pick?
- No. Upload whichever one you have. Our tool reads both and shows you a price either way.
Common questions
- Can I send a STEP or OBJ file instead?
- Not yet. Our upload tool reads STL and 3MF files. If your model is a STEP or OBJ file, export it as an STL or 3MF from your design program first, or ask us for help.
- Which file is smaller?
- STL is usually smaller for one simple part. 3MF can be bigger, because it can carry extra data like color and multiple parts.
- Do I need to know which one to pick?
- No. Upload whichever one you have. Our tool reads both and shows you a price either way.
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