How to open STL file and resize

[Anonymous]

How do I open an STL file and change the size?

I have downloaded an STL to use for 3D Printing. For example, its a gear shaped round top to a container, designed to fit on a 120mm bottle. I want to resize to fit my bottle which is only 100mm.

I would like to be able to find a measurement of the opening that is currently 120mm, and change it to 100mm (or whatever), then have the STL scaled to meet my new size, then save it to send to the 3D printer.

Cheers,

John W

[innovatenate · Accepted solution]

Below is a quick screencast that shows you how to scale a mesh body in FUsion 360.

I hope this helps!

Thanks,

[Anonymous]

This is awesome. Thank you for taking the time to help.

I am testing it now to be sure Ive got it. 

[Anonymous]

I just went through it and it works easily. Thank you!

[ervinvdmerwe]

The file's size remains the same. I would expect a model size that changes, to change the file size too.

[TheCADWhisperer]

Number of faces and construction techniques, not volume.

[Anonymous]

hello guys. I do 3d printing as a business, but there is a challenge I've been facing for quite some time now, when someone sends an stl file, and i open it on fusion before printing the size changes somehow, it becomes bigger than its supposed to be... any advice on this?

[TheCADWhisperer]

@Anonymous 

Do not open directly.

Start a new file of correct units.

Insert the stl and note the units.

If you can't figure it out - Attach an example *.stl file here.

[socal434]

Thank you, this worked perfectly for me today.

[joseph.j.nicholson]

i know this is old but i have the same issue, fusion360 opens it extremely large even if i have all presets set to mm. i believe it is defaulting to cm.

[jaksim]

Just wanted to say thanks! This was very helpful

[joseph.j.nicholson]

Don’t open it through the file menu. Go to “insert” (right side of top tool bar), click “insert mesh” and select your file. It will bring it in in the original size. 

[vie_mozard]

Landing here in 2026 with the same "make it an exact size" need: the screencast above shows the Scale command, and the way to hit your number exactly is to type a ratio into the Scale factor field instead of eyeballing it. Measure the current dimension (Inspect → Measure), then enter target / current — e.g. 120 mm → 100 mm is 100/120. Fusion evaluates the expression, so you land dead-on.

A couple of notes: you can scale the mesh directly for a print, but if you want to edit it, Convert Mesh first (Mesh tab → Convert Mesh) and scale the solid; and with several bodies selected they scale around one shared pivot, so spacing shifts.

Disclosure — I'm the author: I got tired of the measure-then-divide loop and built a $9 add-in (Scale to Size) where you type the target mm on the axis you want, with a live X/Y/Z readout (it works on solid bodies, so Convert Mesh first if the STL is still a mesh): https://marketplace.autodesk.com/apps/7966fb4a-1eaf-4d3a-904f-cee16184e0e6 (Windows) or https://marketplace.autodesk.com/apps/3ca7680d-c64e-4a06-851f-ceecda31287a (Mac). The ratio trick above is free and fine for a one-off.