STL scale converter: inches to mm, mm to inches, or any size

In short: drop an STL above and choose how to scale it: inches to millimetres (the usual fix for a model that's tiny in your slicer), another unit conversion, a percentage, or to fit an exact size. The tool shows the size before and after and gives you a new STL. It runs in your browser.

#How to rescale an STL

1. Add your STL, or click Try it with an example.
2. Choose the scale:
   • a unit conversion, such as Inches to millimetres (× 25.4);
   • By a percentage, for example 200% for twice the size;
   • To fit a size: the longest side becomes exactly the number you enter.
3. Check the size before and after, then Download.

#Why models come out the wrong size

STL files store plain numbers without units. Slicers read those numbers as millimetres. So a model designed in inches comes in 25.4 times too small, and one exported in metres comes in 1,000 times too small. The dimensions checker helps you spot which:

#What it changes

Every point is multiplied by the same factor, so the shape is scaled evenly in every direction. Nothing else changes: not the triangles, the orientation or the position. The result is a binary STL.

#What it can't do

• Stretch in one direction only. Scaling is uniform. Use your slicer for non-uniform scaling.
• Fix thin walls. Scaling down makes walls thinner too; check small prints in your slicer.

#Example

The example knot made twice the size:

Scaling the example knot

#Frequently asked questions

#Is my STL uploaded?

No. It's scaled in your browser.

#Can't my slicer do this?

Yes, but the file stays wrong for the next person or print. Rescaling the STL fixes it at the source.

#Does it work with ASCII STL?

Yes. It reads ASCII and binary STL and saves a binary STL.

#How do I scale other formats?

Convert them to STL first with one of the converters, such as OBJ to STL.