Free tool
Free Online STL File Viewer
Open an STL to rotate it, zoom in, switch to wireframe, and check its size. OBJ, 3MF, STEP, and DXF files open here too.
Your file stays on your computer. Nothing is uploaded.
How OpenSpindle works
We tap our partner network. You get the best-match quote.
Upload your part and we tap our network of partner shops to get you a competitive, all-in quote that is the best match for the job.
One upload
A CAD file or a sketch. That is the whole ask on your end.
Your best-match quote
Sourced from the partner shops set up for your exact part.
All-in, on your timeline
Machining, finishing, and shipping detailed to your turnaround.
STL is the most common file format for 3D printing. Drop an .stl file above and it opens in your browser, where you can orbit, zoom, check it in wireframe, and see its overall dimensions. The file is parsed on your computer and is not uploaded anywhere unless you choose to request a quote.
What is an STL file?
An STL file describes the outside surface of a 3D object as a mesh of triangles. The format dates to the first stereolithography 3D printers in the 1980s, which is where the name comes from, and nearly every slicer and 3D printing service reads it.
That simplicity is also its limit. An STL stores only triangles. It has no field for units or material, no standard way to store color, and no true curves. A round hole becomes a ring of flat facets, and finer detail needs more triangles and a bigger file.
How to open an STL file
- In your browser: drop the file into the viewer above. Nothing to install, and the file stays on your computer.
- A slicer: PrusaSlicer, Cura, and Bambu Studio are free and open STL files for print preparation.
- Mesh software: MeshLab (free and open source) opens STL files for inspection and repair.
- Your CAD program: most CAD programs can import an STL as a mesh body, though editing it is harder than editing a solid.
Why an STL comes in the wrong size
STL files have no field for units. A model designed in inches and exported as STL is just a list of numbers, and most software assumes those numbers are millimeters. The result is a part that appears 25.4 times too small, or a millimeter part that appears 25.4 times too large in inch-based software.
This viewer assumes millimeters and labels STL dimensions as approximate. If the size looks wrong by about 25 times, the file was probably exported in inches. Re-export in millimeters, or tell the shop which unit you used.
STL vs 3MF vs OBJ vs STEP
| Format | Geometry | Units | Color and material | Best for |
|---|---|---|---|---|
| STL (.stl) | Triangle mesh | Not stored | No | 3D printing, the widest support |
| 3MF (.3mf) | Triangle mesh | Stored in the file | Yes | 3D printing with colors, multiple parts, and slicer project settings |
| OBJ (.obj) | Polygon mesh | Not stored | Through a separate .mtl file | Visualization and rendering |
| STEP (.step) | Exact solids | Stored in the file | Limited | Machining, sheet metal, molding |
Can a shop machine from an STL?
Sometimes, but it is not ideal. CAM software works best with exact geometry, and a mesh turns every curve into facets, so hole diameters and radii are approximations. For CNC machining, sheet metal, or molding quotes, send a STEP file. For 3D printing, STL or 3MF is standard. See 3D printing services and how to prepare CAD files for a quote.
Capabilities
Capabilities that use STL files
Send an STL to get quotes for any of these processes.
Frequently Asked Questions
Is this STL viewer free?
Is my STL file uploaded?
Does it open ASCII and binary STL files?
Why does my model look faceted?
Can I edit an STL here?
Can I convert an STL to STEP?
Get your part 3D printed
Upload your STL and we source quotes from independent 3D printing shops, kept under a budget you set.
STEP · STL · IGES · DWG · DXF · PDF · and more
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