Resize an STL online
Fix a model that imports too big or too small, convert inch ↔ mm, or scale to an exact size — with a live before/after readout. Free, private, never uploaded.
Capabilities
Everything you need to get the size right
- Drop an STL and instantly see its real X/Y/Z dimensions and triangle count — STL files carry no units, so this is the fastest way to spot a size problem.
- Fix the classic “imported 25.4× too small” bug with one click: Inch → mm. Also mm → inch, cm → mm and m → mm for models exported in the wrong unit.
- Scale by a percentage, or set the longest side to an exact millimetre value and the other axes follow proportionally.
- Live before/after readout so you know the finished size before you download — no guessing in the slicer.
- Uniform scaling preserves the model’s proportions and writes a clean binary STL, ready for any slicer.
- 100% in your browser — the file never leaves your device, there’s no upload, no queue and no account.
Process
How it works
- Drop your STLThe model loads locally and its exact bounding-box size in millimetres is shown immediately.
- Choose how to resizePick a unit fix (Inch → mm etc.), type a scale percentage, or set the longest side to the size you want.
- Download the resized STLCheck the new dimensions, then download a clean binary STL that drops straight into your slicer at the right size.
FAQ
Questions, answered
Why does my STL import at the wrong size?
STL files store only raw coordinates with no unit. If a model was designed in inches but your slicer assumes millimetres, it appears 25.4× too small (and the reverse makes it huge). This tool multiplies every coordinate by the right factor so the file reads correctly everywhere.
How do I convert an STL from inches to millimetres?
Drop the file and click “Inch → mm”. That scales the model by 25.4 so a part designed as 1 inch becomes 25.4 mm. Download the result and it will load at the correct size in any slicer.
Can I set an exact size?
Yes — type the millimetre length you want for the longest side and the tool scales the whole model uniformly to match, keeping the proportions. You can also enter any scale percentage directly.
Does resizing change the shape or quality?
No. Scaling is uniform and lossless — it only multiplies coordinates, so the geometry, triangle count and proportions are unchanged. The output is standard binary STL.
Is my file uploaded anywhere?
No. The STL is read and rewritten entirely in your browser. Nothing is sent to a server, so it works offline and keeps your model private.
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