An STL viewer that runs on your machine, not ours
Most free STL viewers online work by uploading your model to a server, converting it there, and streaming a picture back. That is slow, it queues at busy times, it usually caps file size, and it means a part you may be under NDA about has just been copied onto someone else's hardware.
This one does none of that. The file is read by your browser and drawn with WebGL on your own GPU. There is no upload step, so there is no size limit, no waiting, and nothing to trust us with — open the Network tab and watch it stay silent while a 200 MB mesh loads.
What you get when a model loads
- Exact dimensions — width, depth and height, switchable between mm, cm and inches.
- Volume and surface area — volume is computed from the mesh itself by summing signed tetrahedra, the same approach a slicer takes, not estimated from the bounding box.
- Triangle count — a quick read on whether a model is over-tessellated for what it is.
- Solid weight in PLA — a sanity figure before you go near a slicer.
- A health check — watertight status, open or non-manifold edges, and degenerate triangles.
How to check an STL is printable before you slice it
A mesh is watertight (also called closed, or manifold) when every edge is shared by exactly two triangles. If some edges belong to only one triangle, the surface has a hole in it, and the slicer has to guess what is inside and what is outside. That guess is where mystery hollow parts, missing walls and weird internal voids come from.
This viewer counts those edges directly and reports how many are open or non-manifold. It also counts degenerate triangles — faces with zero area, usually left behind by a bad boolean or a sloppy export — which some slicers tolerate and others choke on.
If the check comes back clean, the file is safe to slice. If it does not, repair it in your CAD tool or a mesh repair pass before spending eight hours of printer time on it.
The other common trap: units
STL files carry no unit information at all. A model authored in inches and exported as STL looks identical to one authored in millimetres — until it prints 25.4 times too small. If the dimensions here look wildly off, that is almost always why, and the viewer flags models that are suspiciously large or small.
Which formats it opens
STL, both binary and ASCII, which is what nearly every slicer and 3D printing site uses. And OBJ, which is what tends to come out of Blender and other modelling packages. Both are parsed natively — no conversion step, no intermediate file.
Then what?
Once you know the model is sound, the next questions are usually how long it will take and what it will cost. The same file works in our print time estimator and 3D printing cost calculator — both also run entirely in your browser, and both share this page's geometry engine, so the volume figures agree exactly.
Frequently asked questions
How do I open an STL file without installing software?
Drop the file onto this page. It opens straight in your browser using WebGL — no install, no account, no plugin. It works on Windows, macOS, Linux, Android and iOS, since anything with a modern browser can render it.
Is my STL file uploaded to a server?
No. The file is read with the browser File API and rendered locally on your own machine. There is no server to send it to. You can open your browser devtools, watch the Network tab while you load a model, and see that nothing is transmitted — which matters if the part is confidential or client work.
What file formats can this viewer open?
STL in both binary and ASCII form, and OBJ. STL is the standard 3D printing format; OBJ is common from Blender and other modelling tools. Both are parsed natively in the browser.
Is there a file size limit?
No hard limit — the constraint is your own device memory rather than an upload cap. Multi-hundred-megabyte meshes load fine on a normal laptop. The manifold check is skipped above 300,000 triangles because it is the expensive part; everything else still runs.
How do I check whether an STL is watertight?
Open it here and read the health check. A closed, printable mesh has every edge shared by exactly two triangles. This viewer counts the edges and tells you how many are open or non-manifold, plus how many degenerate (zero-area) triangles the file contains. Those are the two faults that most often make a slicer produce a broken or hollow result.
How do I find the dimensions of an STL file?
They are shown as soon as the model loads: width (X), depth (Y) and height (Z), switchable between millimetres, centimetres and inches. If the numbers look 25.4x too small, the file was authored in inches — a very common cause of models printing at the wrong size.
Can it calculate the volume of an STL?
Yes. Volume is computed exactly from the mesh by summing signed tetrahedra over every triangle — the same method a slicer uses — and shown in cm³ along with surface area and a solid-weight estimate in PLA. For filament use, print time and cost on your specific printer, send the same file through our print time estimator or cost calculator.
Why does my model look inside-out or hollow?
That usually means flipped face normals or an open mesh. The health check flags it when the solid volume is implausibly small against the bounding box. Repairing normals in your CAD tool or a mesh repair pass will fix it before you waste a print.