Resize an STL to an exact size

1. Drop your STL, OBJ or 3MF above.
2. Type the width, depth or height you need in mm. With proportions locked, the other two follow. Or pick 50%, 150% or 200%.
3. Choose your printer and press As big as fits to fill the bed, or check the size fits.
4. Download the resized STL or 3MF.

Your file is processed on your device. Nothing is uploaded.

STL files store numbers without units, and every slicer reads them as millimetres. A model drawn in inches then opens 25.4 times too small, and one drawn in centimetres 10 times too small. When a file looks tiny, the tool offers the fix: pick the unit it was made in and it's converted to the right size in mm.

3MF files store their unit, so they open at the right size; this mostly happens with STL and OBJ.

Size grows in three directions at once. Twice as big in every direction is 8 times the volume, so roughly 8 times the filament and print time; half size is an eighth. The panel shows the change as you resize.

Scaling changes everything by the same factor, including parts that need a fixed size: screw holes, snap fits, pin and peg sizes, text height and wall thickness. A model resized to 50% may get walls too thin to print. For parts that must fit something, resize in the CAD program that made them, or check the critical sizes after resizing with the STL viewer's measure tool.

Too big for your printer even at the size you need? Split it into parts instead.