STL EDITOR · FREE · NO UPLOAD
STL Editor — Scale, Rotate & Fix Before You Print
Resize to exact dimensions, rotate onto the build plate, mirror, and center — all in the browser. Nothing uploaded. Export the edited model as STL, OBJ, or GLB.
What it does: edits an STL in the browser — scale to exact millimetres, rotate onto the print plane, mirror, and center on the build plate.
Why you need it: most files need a quick pre-slice adjustment (wrong size, wrong face down, off-center) without opening a full CAD program or slicer.
How it works: three.js applies transforms to geometry positions (scale, 90° rotation, mirror, center). Triangle count and topology stay the same. Nothing is uploaded.
Conversion specs
| Input format | STL (binary or ASCII) |
| Output format | STL, OBJ, or GLB |
| Transforms | Scale (proportional or per-axis), rotate 90°, mirror, center on build plate |
| Topology | Unchanged — positions only; no triangles added or removed |
| Units | Dimensions shown and edited in millimetres (slicer convention) |
| Processing | 100% client-side via three.js geometry transforms |
| File size limit | Device RAM only — no server limit |
| Cost | Free, unlimited, no account required |
What this editor does
Most STL files need a quick adjustment before slicing: the model is the wrong size, facing the wrong way, or not centered on the build plate. This stl editor handles those pre-print fixes without opening a full CAD program or slicer.
Scale to dimensions
Type the target size in millimeters — proportional or per-axis.
Rotate for print orientation
Flip the model onto its flattest face to minimize supports.
Mirror
Flip along any axis — useful for making left/right pairs.
Center on build plate
One click to re-center after transforms.
These transforms modify geometry positions without changing triangle count or topology. The original file on your device is never touched — only the in-browser copy changes. Export when you are done.
How to edit an STL file online
Drop the .stl on the editor above. Type target millimetres to scale, rotate 90° onto the print face, mirror if you need a left/right pair, then center. Triangle count does not change — only vertex positions. Export STL, OBJ or GLB when the preview matches the plate. Nothing is uploaded. Holes still need STL repair; this page does not fill them. For a look without transforming, use the homepage STL viewer.
FAQ
Is my STL file uploaded to a server?+
No. The editor runs entirely in this tab with JavaScript and WebGL. There is no upload endpoint — the file never leaves your device. Editing and export both work offline once the page has loaded.
Can I resize an STL to exact dimensions?+
Yes. The dimension fields show the current size in millimeters. Type the target dimension and press Enter — the model scales to match. With proportional lock on (the default), all three axes scale together so the shape is preserved.
How do I orient my model for 3D printing?+
Use the Rotate 90° buttons to flip the model onto its flattest face. The grid in the viewport represents the build plate. After rotating, click Center to re-align the model to the plate.
Does editing change the triangle count?+
No. The free tools (scale, rotate, mirror, center) transform existing geometry without adding or removing triangles. The mesh topology stays the same — only positions change.
Can I undo changes?+
Not yet in the current version. If you need to start over, reload the file. The original file on your device is never modified — only the in-browser copy changes.
What are the Pro tools?+
Pro tools — face selection, hole filling, cut planes, mesh smoothing, and hollowing — are in development. They will be part of STL Mesh Pro, a paid tier for users who need mesh editing beyond basic transforms.
Holes or non-manifold edges? Run the file through STL repair before you print. A dense mesh slices faster after reducing the STL. Need the edited geometry in another format? The STL to OBJ converter writes an indexed mesh for Blender and other editors. For how the format stores triangles, see what an STL file is.