STL Viewer
Open an STL in your browser and see it the way your slicer will: standing on the build plate, in millimetres, with a watertight check before you print. Nothing is uploaded.
- Files stay on your device
- Free, no sign-up
- Mesh check and printer fit
- 14 formats
Drop an STL file to view it
or
STL · STEP · OBJ · 3MF · GLB · glTF · PLY · FBX · DAE · 3DS · AMF · IGES · VRML · ZIP
Opens on your device. Nothing is uploaded.
Opening…
How to open an STL file online
Open the file
Drop one or more .stl files, binary or ASCII, or a .zip of them.
Check size and orientation
The model stands on the plate in millimetres. Switch to inches, or change the file units or up axis if it looks wrong.
Run the checks
Read the mesh check, pick your printer to see whether it fits, and use Measure (M) or Section (X) for a closer look.
Save or convert
Take a PNG screenshot, or save the model as STL, 3MF, OBJ, GLB, PLY or USDZ.
What you can check in STL files
- Real size in mm or inches, volume, and the weight of a solid PLA print
- Watertight check: open edges, non-manifold edges, flipped normals, separate bodies
- Whether it fits 12 popular printers, as placed or turned 90°
- Point-to-point measurements and a cross-section slider
- Binary and ASCII STL; files of a few hundred MB open on most laptops
About STL files
An STL file is a list of triangles and nothing else: no units, no color, no idea which way is up. Slicers assume millimetres and Z up, so this viewer does too. The model lands on a build plate at its real size, and the X, Y and Z readouts match what Bambu Studio, PrusaSlicer or Cura will show.
Before you print, the mesh check welds the triangles and counts open edges, non-manifold edges and flipped faces, the problems behind most "this model has errors" warnings. Pick your printer to see whether it fits the plate, measure between any two points, or slice through it with the section view to check wall thickness.
STL at a glance
Stereolithography (Standard Triangle Language) · .stl
- Stores
- Loose triangles: three corners and a normal each, binary or ASCII
- Color
- None in the standard
- Units
- None written; slicers assume millimetres
- Up axis
- Z, the slicer convention
- File size
- 50 bytes per triangle in binary, about 5 times that as ASCII
- Opens in
- Every slicer, CAD tool and 3D app
Created by 3D Systems in 1987 for the first stereolithography printers, STL is still the format every slicer and print service accepts. It describes a surface as a list of independent triangles, with no shared vertices, units, colors or scene structure.
Tips for STL files
Model lying down?
Some STLs are saved Y up, often from game or animation tools. Switch the up axis to Y and it stands. In the slicer, "Lay on face" (Bambu Studio, OrcaSlicer) or "Place on face" (PrusaSlicer) does the same.
Tiny model?
If an STL measures a millimetre or two, it was probably saved in metres. The viewer suggests the likely unit; slicers ask the same question on import.
Errors in the check?
A handful of open edges is often fine, because slicers close small gaps. Hundreds of open or non-manifold edges can make the slicer skip walls: run the file through Mesh Repair first.