--- title: "Free Online STL File Viewer | OpenSpindle" description: "Open STL files in your browser to rotate, zoom, and check a 3D model's size before printing or quoting. Free, no install, and files stay on your computer." canonical: https://openspindle.com/tools/stl-viewer --- # 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. 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](/capabilities/3d-printing) and [how to prepare CAD files for a quote](/blog/cad-files-for-quoting). ## Capabilities that use STL files Send an STL to get quotes for any of these processes. - [3D Printing](https://openspindle.com/capabilities/3d-printing.md) - [FDM / FFF 3D Printing](https://openspindle.com/capabilities/fdm-3d-printing.md) - [SLS 3D Printing](https://openspindle.com/capabilities/sls-3d-printing.md) - [MJF 3D Printing](https://openspindle.com/capabilities/mjf-3d-printing.md) - [Resin (SLA/DLP) 3D Printing](https://openspindle.com/capabilities/resin-3d-printing.md) - [PolyJet 3D Printing](https://openspindle.com/capabilities/polyjet.md) - [Metal 3D Printing](https://openspindle.com/capabilities/metal-3d-printing.md) - [Urethane Casting](https://openspindle.com/capabilities/urethane-casting.md) ## More free tools and charts - [Free STEP file viewer](https://openspindle.com/tools/step-viewer.md): Rotate and measure 3D CAD parts in your browser. - [Free DXF and DWG viewer](https://openspindle.com/tools/dxf-viewer.md): See the size and cut length of flat drawings. - [3D printing tolerance chart](https://openspindle.com/reference/3d-printing-tolerance-chart.md): Typical accuracy and minimum wall thickness by process. ## Frequently asked questions ### Is this STL viewer free? Yes. There is no account, no install, and no limit on how many files you open. Files up to 25 MB are supported. ### Is my STL file uploaded? No. The file is read and displayed by your browser on your computer. It is only uploaded if you click Get a quote and then submit the request. ### Does it open ASCII and binary STL files? Yes, both. Binary STL files are much smaller than ASCII for the same model. ### Why does my model look faceted? STL stores surfaces as flat triangles, so curves are approximated. Exporting with a finer resolution or smaller chord tolerance adds triangles and smooths curves, at the cost of a larger file. ### Can I edit an STL here? No, this is a viewer. To edit an STL, use a mesh editor such as MeshLab or Blender, or go back to the original CAD model and export again. ### Can I convert an STL to STEP? Many CAD programs can convert an STL to STEP, but a basic conversion keeps every triangle as a flat face. For a true solid with exact curves, export STEP from the original CAD model.