Private by design
Files open in your browser and are never uploaded, so unreleased designs stay on your device.
Online STL Viewer with Real Dimensions
Open any STL in your browser to rotate it, measure it and check it is watertight before you print. Nothing uploaded.
Loading 3D preview
Drag to rotate
Open a file to see its size, triangle count and whether it is watertight.
Opened in your browser. Files are never uploaded.
Continue with your STL
Pick the next tool for what you want to do with the file.
How to view an STL file online
Open the file, turn it around, then check the numbers your slicer will use.
- 1
Open the STL
Drop a binary or ASCII STL, or several to flip between them.
- 2
Rotate and inspect
Drag to orbit, scroll to zoom, and switch on wireframe to see the mesh density.
- 3
Read the numbers
Check size, triangles, volume and the watertight result before you slice.
Why use this STL viewer
The checks you need before you slice, in any browser.
Real size
Width, depth and height in millimeters or inches, as the slicer will read them.
Watertight check
Counts open and non-manifold edges, the usual cause of failed slices and missing layers.
Volume and filament
Solid volume and a PLA weight estimate, so you know roughly how much filament it takes.
Wireframe view
Switch on wireframe to see how dense the mesh is before it slows your slicer down.
Several files at once
Drop a batch of STL files and flip between them. Binary and ASCII both open.
What's inside an STL file
Every STL viewer and STL reader works from the same short list of data. Knowing it explains most surprises.
Triangles, nothing else
Each facet is three corner points plus a direction. Curves are made of many small flat faces, which is why a coarse export looks faceted.
Numbers without a unit
The file never says millimeters or inches. Slicers assume millimeters, so a model exported in meters shows up 1000 times too small.
No standard color
STL has no standard field for color or materials, so it prints in whatever filament you load. For colors or several parts, use 3MF instead.
Binary or ASCII
Binary STL stores each triangle in 50 bytes; ASCII spells it out as text and is several times larger. This viewer opens both.
Who uses an STL viewer
Different people open STL files for different checks.
Makers downloading models
Check a model from Printables, Thingiverse or MakerWorld for size and holes before it reaches the slicer.
Print services and farms
Open a customer file on any computer to estimate filament and catch broken meshes before printing.
Designers and students
Check an export from Blender, Fusion or Tinkercad on a computer without a slicer installed.
Phone and tablet users
Open an STL from email or chat on the go. The viewer runs in mobile browsers too.
STL viewer questions
Answers about privacy, file size, watertight meshes and the filament estimate.
How do I open an STL file without software?
Drop it onto this page. The STL viewer runs in any modern browser on Windows, macOS, Linux, Android and iOS, with nothing to install.
Is my STL uploaded?
No. The file is read in your browser and never leaves your device.
What does watertight mean?
Every edge of the mesh is shared by exactly two triangles, so the surface encloses a solid. Open edges are holes that confuse slicers and cause missing walls.
Can it open large STL files?
Files up to 300 MB load, though very dense meshes take a few seconds. Binary STL loads faster than ASCII.
Is the filament estimate accurate?
It assumes a solid PLA print. Real prints use infill, so expect noticeably less filament than the estimate for large, chunky models.