# STL Editor

> An STL editor is a tool that changes an existing 3D-print file, such as its size, units or orientation. Kenerate's free online STL editor works in your browser: set an exact size in millimetres, convert inches, rotate 90°, mirror and centre the model on the bed, with undo. Booleans, cutting and repairs aren't included.

URL: https://kenerateai.com/stl-editor
Publisher: Kenerate AI (https://kenerateai.com)
Last updated: 2026-10-01

## Key facts
- Price: Free, no account
- Files: Opens STL, OBJ, 3MF, GLB, FBX, PLY (up to 200 MB) · saves STL, 3MF, OBJ, GLB, PLY
- Size and units: Exact X / Y / Z in mm, proportional lock · inch, cm or m → mm, mm → inch
- Orientation: Rotate ±90° on X / Y / Z; mirror on any axis
- Placement: Centred and dropped to Z = 0 after every edit; undo up to 12 steps
- Not included: Boolean, cut, hollow, repair, sculpting
- Model 25× too small?: It was modelled in inches. STL has no units, so slicers read inches as millimetres — one click scales ×25.4.
- Exact size: Type the width, depth or height you need in millimetres; the others follow when proportions are locked.
- Right side down: Rotate 90° on any axis; the model is re-centred and placed flat on the bed every time.
- Mirror properly: Make a left from a right. Triangle winding is flipped too, so the mirrored mesh isn't inside-out.
- Undo: Step back through up to 12 edits.
- Save in any format: STL, 3MF (with millimetre units), OBJ, GLB or PLY.
- Load: The file is parsed and turned to Z-up print coordinates.
- Transform: Scale, rotation or mirror is applied to every vertex.
- Fix winding: After a mirror, triangle order is reversed so normals point outward.
- Place: The model is centred on X/Y and dropped to Z = 0, ready for a slicer.
- STL (Stereolithography): Triangle mesh (binary or ASCII); by 3D Systems, 1987. Holds: Triangle surfaces, Facet normals. Lacks: Colour and textures, Units, Materials. Best for: 3D printing — every slicer opens it. Opens in: Cura, PrusaSlicer, Bambu Studio, OrcaSlicer, Blender.
- 3MF (3D Manufacturing Format): ZIP package with XML; by 3MF Consortium, 2015. Holds: Meshes with units (millimetres), Colours and materials, Several objects and build plates. Lacks: Animation. Best for: Modern 3D printing and multi-colour prints. Opens in: Bambu Studio, PrusaSlicer, OrcaSlicer, Cura, Windows 3D Builder.
- OBJ (Wavefront OBJ): Plain-text mesh; by Wavefront Technologies, 1980s. Holds: Vertices, faces, UVs and normals, Materials via a separate .mtl file. Lacks: Animation and rigs, Embedded textures. Best for: Moving static meshes between 3D apps. Opens in: Blender, Maya, 3ds Max, ZBrush, most slicers.
- Resize, units, rotate, mirror: This editor: Yes | Use instead: —
- Change a hole's diameter: This editor: No (it's triangles, not a parameter) | Use instead: CAD with the original design, or remodel
- Cut, combine, subtract: This editor: No | Use instead: Your slicer's cut tool, Blender, Meshmixer
- Repair holes / non-manifold: This editor: No | Use instead: Slicer auto-repair, Blender 3D-Print Toolbox
- Change text on a model: This editor: No | Use instead: Remodel the text with the 3D Text Generator, then combine

## Steps
1. Open a file — Drop an STL (or OBJ, 3MF, GLB, FBX, PLY) onto the box above.
2. Fix units and size — Click inch → mm if it's tiny, or type the exact size you need.
3. Orient — Rotate 90° until the flattest side is down; mirror if you need the opposite hand.
4. Download — Save STL or 3MF and slice.

## In depth

### Mesh, not CAD
STL stores only triangles — no units, no features, no history [1]. That makes scaling and rotating easy and changing a hole's size hard. For design changes, go back to the CAD file or remodel the part.

### Units
Slicers assume millimetres. Files from inch-based tools arrive 25.4× too small; files exported in metres arrive 1,000× too small. Converting once and saving as 3MF, which stores millimetres, prevents it next time [5].

### Printable after editing
Scaling down thins every wall. Keep walls at or above about 0.9 mm on a 0.4 mm nozzle and remember that fits need around 0.3 mm of clearance [11].

References:
[1] Wikipedia — STL (file format): https://en.wikipedia.org/wiki/STL_(file_format)
[2] Wikipedia — Wavefront .obj file: https://en.wikipedia.org/wiki/Wavefront_.obj_file
[3] Wikipedia — FBX: https://en.wikipedia.org/wiki/FBX
[4] Khronos Group — glTF: https://www.khronos.org/gltf/
[5] 3MF Consortium — 3MF specification: https://3mf.io/specification/
[6] Wikipedia — Universal Scene Description (USD / USDZ): https://en.wikipedia.org/wiki/Universal_Scene_Description
[7] Wikipedia — PLY (file format): https://en.wikipedia.org/wiki/PLY_(file_format)
[8] Khronos Group — glTF 2.0 specification: https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html
[9] Apple — AR Quick Look: https://developer.apple.com/augmented-reality/quick-look/
[10] three.js — documentation: https://threejs.org/docs/
[11] Prusa Knowledge Base — Modeling with 3D printing in mind: https://help.prusa3d.com/article/modeling-with-3d-printing-in-mind_164135
[12] Prusa Blog — lithophanes and filament transparency: https://blog.prusa3d.com/lets-play-with-filament-transparency-how-to-make-amazing-lifelike-color-photos-with-just-a-simple-color-change_104338/
[13] Polymers (2024) 16(20):2862 — FFF parameters and translucency of PLA: https://doi.org/10.3390/polym16202862
[14] Wikipedia — Lithophane: https://en.wikipedia.org/wiki/Lithophane
[15] W3C — CSS Values and Units Level 3 (absolute lengths): https://www.w3.org/TR/css-values-3/
[16] Adobe Substance 3D — OpenGL vs DirectX normal maps: https://experienceleague.adobe.com/en/docs/substance-3d/bakers/common-questions/what-is-the-difference-between-the-opengl-and-directx-normal-format
[17] Blender Manual — Normal Map node: https://docs.blender.org/manual/en/latest/render/shader_nodes/displacement/normal_map.html
[18] Wikipedia — Normal mapping: https://en.wikipedia.org/wiki/Normal_mapping
[19] SIL Open Font License: https://openfontlicense.org/

## FAQ
Q: Is this STL editor free?
A: Yes. It's free, needs no account and runs in your browser.

Q: Why does my STL open 25 times too small?
A: It was made in inches. STL has no units, so your slicer reads 1 inch as 1 mm. Click “inch → mm” to scale it by 25.4.

Q: Does editing reduce quality?
A: No. Scaling, rotating and mirroring move the same triangles; nothing is simplified.

Q: Should I scale here or in my slicer?
A: Either works for printing. Editing here gives you a corrected file to share or keep, in any format.

Q: Will non-uniform scaling break holes?
A: It can: stretching one axis turns round holes oval and changes fits. Keep proportions locked for parts that must fit other parts — moving parts need about 0.3 mm clearance.

Q: Can I edit text or features in an STL?
A: Not directly — an STL has no features, only triangles. Model the new part separately and combine it in a slicer or mesh editor.

Q: Is my file uploaded?
A: No. It's edited on your device.

Q: Are STL files editable?
A: Yes, as meshes. You can resize, rotate and mirror them here, or cut, combine and sculpt them in Blender or a slicer. What you can't do is change design features like a hole's diameter, because an STL stores only triangles — for that you need the original CAD file.

## Related pages
- AI 3D Model Generator: https://kenerateai.com/ai-3d-model-generator
- Image to 3D: https://kenerateai.com/image-to-3d-converter
- AI STL Generator: https://kenerateai.com/ai-3d-printing-model-generator
- Text to 3D: https://kenerateai.com/text-to-3d-generator

## Sources
- Wikipedia — STL (file format): https://en.wikipedia.org/wiki/STL_(file_format)
- Wikipedia — Wavefront .obj file: https://en.wikipedia.org/wiki/Wavefront_.obj_file
- Wikipedia — FBX: https://en.wikipedia.org/wiki/FBX
- Khronos Group — glTF: https://www.khronos.org/gltf/
- 3MF Consortium — 3MF specification: https://3mf.io/specification/
- Wikipedia — Universal Scene Description (USD / USDZ): https://en.wikipedia.org/wiki/Universal_Scene_Description
- Wikipedia — PLY (file format): https://en.wikipedia.org/wiki/PLY_(file_format)
- Khronos Group — glTF 2.0 specification: https://registry.khronos.org/glTF/specs/2.0/glTF-2.0.html
- Apple — AR Quick Look: https://developer.apple.com/augmented-reality/quick-look/
- three.js — documentation: https://threejs.org/docs/
- Prusa Knowledge Base — Modeling with 3D printing in mind: https://help.prusa3d.com/article/modeling-with-3d-printing-in-mind_164135
- Prusa Blog — lithophanes and filament transparency: https://blog.prusa3d.com/lets-play-with-filament-transparency-how-to-make-amazing-lifelike-color-photos-with-just-a-simple-color-change_104338/
- Polymers (2024) 16(20):2862 — FFF parameters and translucency of PLA: https://doi.org/10.3390/polym16202862
- Wikipedia — Lithophane: https://en.wikipedia.org/wiki/Lithophane
- W3C — CSS Values and Units Level 3 (absolute lengths): https://www.w3.org/TR/css-values-3/
- Adobe Substance 3D — OpenGL vs DirectX normal maps: https://experienceleague.adobe.com/en/docs/substance-3d/bakers/common-questions/what-is-the-difference-between-the-opengl-and-directx-normal-format
- Blender Manual — Normal Map node: https://docs.blender.org/manual/en/latest/render/shader_nodes/displacement/normal_map.html
- Wikipedia — Normal mapping: https://en.wikipedia.org/wiki/Normal_mapping
- SIL Open Font License: https://openfontlicense.org/