Merge STL Files

Open all the STL files at once (or add them one by one), choose a layout and click Download merged STL. The triangles of every file are written into one STL in the positions you see on the plate. Nothing is resized or changed.

Side by side drops every file onto the plate and lays them out next to each other, which is what you want for printing several separate models in one go. Positions from the files restores the coordinates each STL was exported with, so parts exported separately from one CAD assembly (for example the pieces of a multi-color print) line up exactly again. The group is then moved onto the middle of the plate without changing how the parts sit relative to each other.

No. The files are combined into one file, not fused with a boolean union. Parts that overlap keep their own surfaces, which slicers handle fine for printing. If you need a single watertight solid, combine the parts with union() in CAD such as the OpenSCAD playground.

A merged STL opens as one object, which is handy for print services and tools that accept one file. Download the 3MF to keep each file as a separate named object, so a slicer like Bambu Studio, PrusaSlicer or Orca lets you set colors, filaments or settings per part. Most slicers can also split a merged STL back into parts.

STL files store bare numbers without units. A part exported in inches shows up 25.4 times too small next to parts in millimeters. Fix that part on the Resize STL page (its unit buttons convert inches, centimeters and meters to millimeters) or in the full mesh editor, then come back; your files stay loaded.

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.