STL Unit Converter & Scaler
Scale STL 3D models or convert units (mm/cm/m/inch). Reads binary and ASCII STL. Applies scaling factor or per-axis scaling. Runs in your browser — models never upload.
Upload .stl file
Binary or ASCII, any size your browser can handle
STL Unit Converter & Scaler Tutorial
What This Does
Your STL model is in the wrong units? Maybe imported a Solidworks export as inches when your slicer expects mm? This tool scales every vertex in the file by a factor you specify — uniform or per-axis — and re-serializes either as binary STL (compact, fast) or ASCII STL (human-readable, bigger).
Common Conversions
- inch → mm (×25.4) — most common, US-source models to metric slicers (Cura, PrusaSlicer)
- m → mm (×1000) — CAD defaults like Fusion 360 sometimes use meters
- mm → cm (÷10) — less common but happens with old exports
- Uniform scale (e.g. ×2) — enlarge or shrink a print
Per-axis Scaling
Useful for correcting anisotropic stretch (e.g. if your 3D scanner output is slightly off in Z). Leave X/Y/Z at 1 to use the uniform factor.
STL Format Notes
- Binary STL — 80-byte header, 4-byte triangle count, 50 bytes per triangle (normal + 3 vertices, all float32 little-endian, plus 2-byte attribute). Most common format.
- ASCII STL — starts with
solid name, each triangle asfacet normal ... vertex ... vertex ... vertex .... Readable but 5× larger.
Normals are recomputed when you apply per-axis scaling (non-uniform scale changes face orientation); for uniform scaling the normals stay the same.
Why In-Browser?
STL files can be big (10-100+ MB) and you don't want to upload a product design to a random website. This tool parses the binary format in JavaScript, applies the scale, and saves locally. Nothing touches our server. Open DevTools → Network and you'll see no requests.
What This Doesn't Do
- Preview the 3D model (use viewstl.com or 3dviewer.net)
- Repair broken STLs (use Meshmixer)
- Convert to other formats (3MF, OBJ) — separate job
- Decimate / simplify geometry