●
3DAI
Free · runs in your browser · no signup

Scale or Resize an STL File

Make a model bigger or smaller before you print or share it. Scale it by a percentage, type the exact size you need on one axis and let the others follow, or fix a model that was drawn in inches and opens tiny in your slicer. The new size is shown live and the file never leaves your computer.

Loading the converter...

How to use it

  1. 1

    Add your STL

    Drop a binary or ASCII .stl on the box or click to pick it. The current size is shown in mm.

  2. 2

    Choose how to resize

    Percent scales all axes together. Exact size sets width, depth or height. Convert units multiplies by 25.4, 10 or 1000.

  3. 3

    Check the new size

    The preview and the size readout update as you type, so you can see the result before saving.

  4. 4

    Download the STL

    Save the scaled STL as binary (small) or ASCII and open it in your slicer.

What to know before you convert

  • Scaling multiplies every coordinate. It does not keep holes, threads or wall thickness at a fixed size: a 3 mm hole in a model scaled to 200% becomes 6 mm.
  • Without "keep proportions", each axis is scaled on its own, which stretches round features into ovals.
  • STL has no unit field. Slicers read the numbers as millimetres, so "inches to mm" multiplies them by 25.4.
  • Only STL files are accepted. Very large files depend on your device memory; 100 MB is the upper limit.

Don't have a model?

Create one with AI from a photo, a sentence or a sketch. The generators use credits; this converter is free and stays in your browser.

Image to 3D →Turn one photo into a textured 3D model.Text to 3D →Describe an object and get a GLB.Sketch to STL →Draw it, get a printable model.

Frequently Asked Questions

Drop it on the box above, choose Percent, Exact size or Convert units, and download. The scaling runs in your browser with three.js, so nothing is installed or uploaded.
It was most likely drawn in inches. STL stores bare numbers and slicers read them as millimetres, so a 2 inch part shows up as 2 mm. Choose Convert units, pick inches to millimetres (x 25.4) and save the file.
Choose Exact size, keep "Keep proportions" ticked and type the height in the Height (Z) box. Width and depth follow at the same ratio. Untick it to set each axis on its own.
Yes. Every dimension is multiplied by the same factor, holes and pegs included. If parts must fit a screw or a bearing, scale in your CAD program instead, where you can keep those features fixed.
No. The page reads the file and converts it inside your browser with the open-source three.js library. Nothing is sent to our servers, there is no account, and no credits are used. Closing the tab discards everything.