Guide
How to open an STL file and check it for 3D printing
Drop the .stl file on Anyfile’s 3D viewer and the model appears on a floor grid you can orbit around. Check for printing then says whether it’s closed and ready to print, with its volume and weight in PLA. Repair fixes common faults, and you can set an exact size before saving.
Step by step
Open the model
Drop the .stl on the 3D viewer, or on the STL page and choose Edit file. Binary and text STL both open, stood upright the way printers keep them.
Look all the way round
Drag to orbit, and scroll or pinch to zoom. The Front, Top and other views line it up square, and Fit brings it back.
Check it for printing
Choose Model › Check for printing (Print check on the toolbar). It reports Ready to print or Not closed, with open edges and edges shared by three or more faces, and the volume in cm³ with a weight in PLA.
Repair it, if it needs it
Model › Repair: join corners and fix normals merges duplicate corners, drops collapsed triangles and works out the normals again, keeping sharp edges. Check again afterwards.
Set the size and save
Exact size on the toolbar sets Width (mm), Depth (mm) and Height (mm), keeping proportions if you like. Then press Download for STL, or open the arrow next to it and choose 3MF or another format.
STL files don’t say what unit they’re in. If a model arrives tiny or enormous, it was probably drawn in inches or metres: set Units in the file to the right one, rather than scaling by guesswork. Saved STLs are in millimetres.
Repair fixes the small faults that confuse slicers. It doesn’t fill large holes, and a model can still be Not closed afterwards; then it needs fixing in the app it came from.
Nothing is uploaded: your browser reads the file and makes the new one on your device. See how it works, and how to check.
Other ways to do it
A slicer. PrusaSlicer, Cura and Bambu Studio are free, open STL files, and show exactly how a print will be laid down. If you’re printing it anyway, that’s where the model ends up.
On a Mac. Quick Look and Preview can show many 3D models: select the file and press Space to see whether yours opens.
Modelling apps. Blender and CAD apps open STL for real changes to the shape itself.
When Anyfile is quicker
Anyfile is quicker for a look at a model someone sent you, a print check on a computer without a slicer, or a resize and conversion to 3MF in a minute. For preparing the actual print, use your printer’s slicer.
Questions
What does closed mean, and why does it matter?
Every edge is shared by exactly two triangles, so the model has a clear inside and outside. Slicers need that to know what to fill.
Why is my model the wrong size?
STL has no units. Set Units in the file to what it was drawn in, such as inches, and it’s shown at its real size.
Can I save it as 3MF or OBJ?
Yes. Choose the format with the arrow next to Download; 3MF keeps each part’s colour, STL doesn’t.
Is the model uploaded?
No. It’s opened and saved by your browser, on your device.