How to resize a model on an iPad

You can resize a downloaded model on an iPad without installing anything: open Handoff3D in Safari, choose the file, and type the size you want in millimetres. It shows you the model at that size on your printer's own bed and saves a print-ready file into Files. The whole thing happens in the browser tab — your model is never uploaded.

Free, no account, nothing installed. Works in Safari on an iPad or an iPhone.

Step by step

1. Get the file onto the iPad. Downloading from MakerWorld, Printables or Thingiverse in Safari puts it in Files, under Downloads.
2. Open the page and tap Choose a model. iOS offers Photo Library and Take Photo first — you want Choose File, the third row down.
3. Pick your printer. The bed drawn underneath the model changes to match, so you can see immediately whether the thing fits.
4. Set the size. Type a measurement in millimetres, or drag the slider. Across, deep and tall are all shown, so you can size by whichever one matters — the height of a figure, the width of a bracket, the diameter of a lid.
5. Save it. Out comes a Bambu project file, and a page of instructions for getting it to the printer.

Size by the measurement that matters, not by percent

Most resizing goes wrong because it is done as a percentage. "Scale to 140%" tells you nothing about whether the result fits the shelf. Here you give the real measurement, in millimetres, and the other two directions follow proportionally.

One thing worth knowing if your model arrived tipped or lying on its side: the sizes are measured against the model as it will stand on the plate, not against however the file happened to be saved. So "tall" is the height it will actually print at.

If it is too big for the bed

Scaling down is not the only way out. A model larger than your bed can be cut up and spread over as many plates as it needs, then printed in pieces — see when a model is too big for the bed.

Which files it will open

STL, 3MF, OBJ and PLY — the four formats models are actually published in. A 3MF exported by Bambu Studio or OrcaSlicer opens fine.

Common questions

How do I scale an STL on an iPad?

Open Handoff3D in Safari, choose the STL from your Files app, and enter the size you want in millimetres. It writes a resized, print-ready file back into Files. Nothing is installed and the model is not uploaded.

Can I resize a 3MF without a computer?

Yes. 3MF is one of the four formats it reads, alongside STL, OBJ and PLY, and the file it writes back out is a Bambu project file.

Does resizing in a browser lose quality?

No. Scaling a model is arithmetic on its coordinates. The shape is described mathematically, so it comes out as the same shape at a different size, with nothing thrown away.