How to open STL files on any device

You downloaded a model from Printables, Thingiverse or MakerWorld, or a customer emailed you a part, and your computer shows a blank icon with ".stl" on the end. STL is a plain list of triangles that describes a 3D surface (see STL files explained), and almost every 3D program can read it — but operating systems have become less helpful, not more. Microsoft has retired its built-in 3D apps, and phones have never shipped a dedicated STL viewer. This guide covers the fastest option for each device.

The quickest way on any device: a browser viewer

A modern browser can draw 3D graphics with WebGL, so an STL viewer can run as a web page. Our online STL viewer works in Chrome, Edge, Firefox and Safari on Windows, macOS, Linux, iPhone, iPad and Android:

1. Open the STL viewer.
2. Drag the .stl file onto the page, or tap Open STL file and pick it from your downloads, Files app or cloud drive.
3. Drag to rotate; click the model and scroll, or pinch, to zoom; double-click to reset the view.

The file is read by JavaScript on your own device and is never uploaded, so it is safe for unreleased designs and customer files. Besides the 3D view you get the model's dimensions, volume, surface area and triangle count, a watertight check that finds holes and flipped faces, and — further down the page — an estimate of the filament and cost to print it. Binary and ASCII STL both work, including large files with a million triangles or more.

If you only need to look at a model occasionally, this is all you need. The sections below are for people who want a native app or more editing power.

Windows 10 and Windows 11

For years the answer on Windows was "double-click it": Windows 10 shipped with 3D Viewer, and Paint 3D and 3D Builder could open STL as well. That era is over:

• Paint 3D was deprecated in 2024 and removed from the Microsoft Store in November 2024.
• 3D Viewer was deprecated in early 2026 and removed from the Microsoft Store on July 1, 2026. If it is already installed it may still open files, but it cannot be installed again and gets no updates. Microsoft's own suggestion for viewing 3D content is the web-based Babylon.js Sandbox.
• 3D Builder has also disappeared from the Microsoft Store.

So on a current Windows PC, use a browser viewer for a quick look, or install a free slicer. PrusaSlicer, UltiMaker Cura, Bambu Studio and OrcaSlicer all open STL files, show them on a virtual print bed and let you scale, rotate and cut them — and you will need one of them anyway if you plan to print. To set a default app, right-click the file, choose Open with → Choose another app, select the slicer and tick "Always use this app".

macOS

Macs are the exception: Apple's Preview app lists STL among the 3D formats it can open, so double-clicking an STL normally shows it in a rotatable 3D view with no extra software. In Finder you can also select the file and press the space bar for a Quick Look preview; if your macOS version shows only an icon there, open the file in Preview instead.

One quirk: STL models are usually drawn with Z pointing up, while Apple's 3D frameworks treat Y as up, so a model may appear lying on its back. That is a display convention, not a problem with the file — slicers and our viewer show it standing on the bed. For measurements, mesh checks or printing, use the browser viewer or one of the slicers above, all of which have macOS versions.

iPhone and iPad

iOS and iPadOS do not include an STL viewer. Apple's Quick Look framework, which powers previews in the Files app and Mail, is documented for USDZ 3D models rather than STL, so tapping an STL attachment usually just offers to share or save it. Your options:

• Safari: open the online STL viewer, tap Open STL file and choose the file from Files, iCloud Drive or another storage provider. Pinch to zoom and drag with one finger to rotate.
• App Store viewers: several free and paid STL viewer apps exist. Check recent reviews and whether the app works offline before installing — many are thin wrappers around a web view.

To open an email attachment, save it to Files first, then pick it from the viewer.

Android

Android has no built-in 3D model viewer either. In Chrome, open the online viewer and tap Open STL file; Android's file picker lets you choose files from Downloads, Google Drive and other cloud storage apps. If you prefer an app, the Play Store has dedicated STL viewers — for example a small open-source 3D model viewer by developer Dmitry Brant that registers itself as the handler for .stl files, so tapping one in a file manager or browser opens it directly. As with iOS, read recent reviews before installing anything that asks for broad storage permissions.

Linux

Linux has the widest choice of free, native tools:

• F3D — a fast, minimal, open-source viewer (also on Windows and macOS). Run f3d model.stl or set it as the default app for .stl files.
• fstl — a tiny STL-only viewer that opens even huge files quickly; a maintained fork is available on Flathub.
• MeshLab — for inspecting and repairing meshes: measure, close holes, simplify and convert formats.
• FreeCAD and Blender — import STL for editing. FreeCAD loads it as a mesh, which its Mesh Design workbench can convert to a solid; Blender treats it like any other mesh.
• PrusaSlicer, Cura and OrcaSlicer — available as AppImage or Flatpak packages, for when you want to print.

Which option should you use?

When an STL won't open or looks wrong

• The model is a tiny speck or enormous. STL has no units. Most files are in millimetres, but some are exported in metres or inches; change the units in the viewer or slicer.
• Parts of the model are red or see-through. In our viewer red shows the inside of the surface. Seeing it from outside means holes or flipped triangles; the mesh check lists them, and slicers or MeshLab can usually repair them.
• "Not a valid STL file." Check that the download finished and that the file really is STL: model sites often offer 3MF, OBJ or a ZIP archive of several STLs. Unzip archives first.
• The file is huge and slow. Scanned and sculpted models can have millions of triangles. A browser viewer handles a million triangles in a few seconds on a modern computer; for larger files use F3D or a slicer, or simplify the mesh in MeshLab.
• You want to edit it like a CAD model. STL stores only triangles, not the original features, so CAD programs open it as a mesh. Ask the designer for a STEP file if you need to change dimensions precisely.

Once the model looks right, the same page tells you what it costs to print: drop it into the 3D print cost calculator for grams, meters of filament, print time and a full price.

Open an STL in the online viewer →