STL vs 3MF vs OBJ: which file should you send for 3D printing?

You have a model and want it printed. Your CAD program offers a dozen export formats, and the print shop accepts three of them: STL, 3MF and OBJ. Which one should you send? The short answer: any of the three works for a single-colour print, and the choice of STL vs 3MF matters less than how you export. The longer answer explains why some files print perfectly and others arrive in the wrong size, with holes, or as a jumble of loose parts.

What a print file has to carry

For a 3D print, a file only has to describe one thing: the closed outer surface of the part. The slicer, the program that turns a model into printer instructions, fills that surface with walls and infill and works out every layer. Everything beyond the surface (colours, textures, materials, units, how parts sit on the plate) is extra information that some formats can carry and others cannot.

STL: the old standard that every program understands

STL dates from 1987 and describes a surface as a list of triangles. Nothing else: no units, no colour, no names. That simplicity is why every CAD program and every slicer supports it.

• Good: universal, simple, almost impossible to open wrongly.
• Watch out: an STL has no units. A part designed in inches arrives 25.4 times too small when the slicer assumes millimetres. Curves are approximated by flat triangles, so a coarse export shows visible facets on round surfaces.

3MF: the modern format that keeps more information

3MF was created by a consortium of 3D printing and software companies as a replacement for STL. It is a small zip archive that stores the mesh together with its units, the position of each part on the plate and, optionally, colours and materials.

• Good: units are stored, so the size is right; files are compact; several parts keep their arrangement.
• Watch out: a 3MF saved from a slicer can contain that slicer’s settings and several build plates. We price and print one plate per model, so export just the part, not a full multi-plate project.

OBJ: common in 3D art and games

OBJ comes from computer graphics. It stores a mesh with optional texture coordinates and material references, which is why sculpting and game-art tools use it. For printing, only the geometry counts.

• Good: easy to export from Blender, ZBrush and most art tools.
• Watch out: like STL, OBJ has no reliable units, and models made for games are often open surfaces or overlapping pieces rather than one closed solid. That is the difference we describe in game-ready vs print-ready models.

STL vs 3MF vs OBJ at a glance

In short, STL vs 3MF comes down to units and extra information; OBJ sits in between and depends on where it came from.

Export settings that matter more than the format

Whichever side of STL vs 3MF you choose, these settings decide whether the print comes out right:

1. Units in millimetres. Check the size in the exported file, not only in your CAD program. Our quote shows the size of your part, so you can see straight away if it came out 25 times too small.
2. Enough resolution. Use a fine chord or deviation setting for curved surfaces. A coarse export prints as visible flat facets.
3. Not too much resolution. Millions of tiny triangles add nothing on a printer with a 0.4 mm nozzle and make the file slow to handle. We accept files up to 50 MB and two million triangles.
4. One closed solid. No holes in the surface, no faces pointing inward, no separate shells that overlap. Most CAD programs get this right by themselves; sculpting tools often do not.
5. The right orientation. We print the model the way it lies in your file, so export it with the flattest side down.

How to export from common programs

• Fusion: right-click the body, choose Save as Mesh, pick 3MF or STL, set the units to millimetres and the refinement to High.
• Blender: set the scene units to millimetres, apply all modifiers and the scale, then use File, Export, STL or OBJ with only the selected object.
• Tinkercad: Export, then .STL or .OBJ. Tinkercad works in millimetres, so the size is right.
• SolidWorks and Onshape: export as 3MF where offered; otherwise as STL in millimetres with a fine deviation.

Our advice in one line

Send a 3MF if your program offers it, an STL otherwise, and an OBJ only if that is what your art tool makes, as long as the mesh is one closed solid in millimetres. Our instant 3D print quote accepts all three, shows the size it read from your file and gives you a price in seconds, so you find a units problem before you order, not after.