Resize STL Online

Open the file, type the target width, depth or height in millimeters and click Apply size. With Keep proportions on, the tool computes one scale factor from the size you typed (for example 120 mm ÷ 40 mm = 300%) and applies it to all three axes, then you download the scaled STL.

Yes. Turn off Keep proportions and type a size for each axis, for example to make a box taller without making it wider. Holes and text get stretched too, so round holes become oval; for parts that must mate with screws or other parts, resize proportionally or change the original design instead.

Yes, everything scales by the same factor. A 3 mm screw hole in a model scaled to 200% becomes 6 mm, and 1.2 mm walls become 2.4 mm. If a part has to fit a specific screw or bearing, check those features after resizing, or edit the source CAD file.

STL files store bare numbers without units, and slicers read them as millimeters. A model exported in inches shows up 25.4 times too small, and one exported in meters 1000 times too small. Use Inches → mm, Centimeters → mm or Meters → mm to correct it.

The result is the same size, but here the scale is written into the file itself. That helps when you share the STL, upload it to a print service, or want a fixed-size version without remembering a percentage in every slicer project.

No. Files are read and processed by JavaScript in your browser tab, and downloads are generated locally. Nothing is sent to a server, so it also works with private or unreleased designs.