Make an STL file smaller
By default only what a print cannot show is taken out: the surface moves 0.05 mm at most, finer than a 0.4 mm nozzle draws, so a big model keeps more triangles than a small one. Or choose how many of the triangles to keep and see the file size it will make. Flat and gently curved areas lose triangles first; edges and fine detail are kept to the end, and the page tells you about how far the surface moved.
Saves model files for your slicer, never printer code. Opened and sliced in PrusaSlicer, OrcaSlicer, Bambu Studio and Cura.
Why STL files get big
An STL stores every triangle on its own: 50 bytes each, so a million triangles is 48 MB. Scans and models exported at the finest setting often have far more triangles than any printer can show — a 0.4 mm nozzle does not see detail finer than that.
How much to keep
Start at a quarter. On a test sphere of 32,768 triangles, keeping a quarter moved the surface by about 0.02 mm — a twentieth of a 0.4 mm nozzle line — and changed the volume by 0.15 %. The triangles that are left stay even, so a curved surface stays smooth. Look at the model after reducing; if a detail went soft, Undo and keep more.
Smaller again: 3MF
A 3MF file is compressed and stores each point once, so the same model is usually less than half the size of a binary STL — useful when an upload form accepts 3MF.
Questions
- Tinkercad says my file is too big.
- Tinkercad imports files up to 25 MB. The page shows the STL size before you reduce, so you can pick the share of triangles that brings it under.
- Will it ruin text and sharp edges?
- Edges are kept as long as possible, but at a very low share small text softens first. Keep more triangles, or reduce only the part without text: cut it off, reduce, combine back.