STL Viewer
Open an STL to inspect it from every angle, check its size, volume and print weight, and spot open meshes before you slice.
- Size, volume & weight
- Watertight check
- Section view & measuring
- No upload
Drop an STL file here.
Drag to rotate · scroll or pinch to zoom · right-drag or two fingers to pan
What is an STL viewer?
STL (stereolithography) is the most common file format for 3D printing. It stores a model as a list of triangles, with no colours, materials or units, in either ASCII or binary form. An STL viewer draws those triangles so you can check a model before sending it to a slicer. This viewer goes further: it reports the bounding-box size in millimetres, centimetres, metres or inches, the surface area and volume, estimates the solid weight and filament length for PLA, PETG, ABS, TPU or resin, and checks whether the mesh is watertight (every edge shared by exactly two triangles), which slicers need for reliable prints.
How to view an STL file
- Choose Open File and pick your STL (add its textures or material files too), or drag them onto the viewer.
- Drag to rotate, scroll or pinch to zoom, and right-drag or two-finger drag to pan.
- Switch between shaded, wireframe and X-ray, use the view buttons, or cut a section to see inside.
- Read the size, volume and triangle count, measure between two points, then export or take a snapshot.
Tips for checking a print
- STL has no units. Most printing files are in millimetres; if a model looks 25 times too small, it was probably exported in inches.
- A watertight mesh is required for an accurate volume. If the check fails, repair the model in your slicer or in Meshmixer.
- Use the section view to check wall thickness and hidden internal geometry.
- Weight estimates assume 100% infill; with typical 15–20% infill and walls, expect 30–50% of the solid weight.
Why use this STL viewer
- Measure, not just lookDimensions, triangle count, surface area, volume and a watertight check, plus click-to-measure distances and a section view.
- Print estimatesSolid weight and 1.75 mm filament length for common materials, from the exact mesh volume.
- Watertight checkFind holes and non-manifold edges that cause slicing errors, before you waste a print.
- Your model stays on your deviceFiles are read and rendered in your browser with WebGL. Nothing is uploaded, so unreleased products, client work and scans stay private.
Supported 3D formats
| Format | Files | Typical use |
|---|---|---|
| STL | .stl | Triangles only (ASCII or binary); the standard for 3D printing |
| 3MF | .3mf | Modern print format with objects, colours and units |
| OBJ | .obj + .mtl | Text format from modelling tools; materials and textures in separate files |
| glTF / GLB | .gltf, .glb | Web and AR standard with PBR materials and animations |
| FBX | .fbx | Autodesk exchange format for animation and game engines |
| PLY | .ply | Scans and point clouds, often with vertex colours |
| Collada, 3DS, AMF, VRML | .dae, .3ds, .amf, .wrl | Older exchange and print formats |
Common uses
- Before slicing. Check orientation, scale and holes.
- Downloads from Thingiverse or Printables. Preview files without installing software.
- Quoting prints. Get volume and weight for pricing.
- CAD exports. Confirm an export from Fusion, SolidWorks or Onshape came out right.
More file tools: view SVG images as PNG, inspect photo metadata or convert images to ICO icons.
Example: estimating a print
Open a 60 × 40 × 25 mm bracket. The viewer reports 18.4 cm³, watertight. At PLA’s 1.24 g/cm³ the solid weight is 22.8 g, about 7.7 m of 1.75 mm filament, before infill savings.
What to expect from the result
Colour STL variants are shown when present. Volume and weight assume a closed mesh. Extremely large files are limited by your browser’s memory.
STL Viewer questions
How do I open an STL file without software?
Choose Open File and pick the .stl, or drag it onto the viewer. It opens instantly in your browser on Windows, macOS, Linux, Android or iOS.
What units are STL files in?
STL files have no units. 3D printing files are usually in millimetres, so the viewer assumes mm; switch to cm, m or inches if the size looks wrong.
How is the volume calculated?
The viewer adds up the signed volumes of tetrahedra formed by each triangle, the standard method for closed meshes. It is only meaningful when the model is watertight, which the viewer checks for you.
What does “watertight” mean?
Every edge of the mesh is shared by exactly two triangles, so the surface is closed with no holes. Slicers and volume calculations need watertight meshes.
Are my 3D files uploaded?
No. The viewer runs entirely in your browser using WebGL; the file is never sent to a server and the page keeps working offline once loaded.