STLBenchFree online STL editor
STL editor that measures before it converts
Drop an STL and get the numbers first: click two points for a distance in millimetres, slide a section plane through the part to check wall thickness, and toggle wireframe to see the topology a shaded view hides. When you know what the file holds, convert it to OBJ, 3MF, GLB or PLY — still in the browser, still with nothing uploaded. This is the editing that matters before a mesh reaches a slicer or a modeller: knowing what is in it and getting it into the right format.
- 100% free
- No signup
- Measure and section
- Six export formats
- Nothing uploaded
Drag a file anywhere on this page to open it. F fits the view, W switches shading, G the grid, R spins it, M measures.
How to edit an STL file
Three steps — inspect, measure, convert.
Drop the STL
Binary or ASCII, any size your browser can hold in memory. The file stays local — there is no upload step, no queue and no server involved. The panel underneath shows the triangle count, bounding box and whether the mesh is closed, which matters because an open mesh cannot be sliced for printing without repair.
Measure and section
Click any two points on the surface to get a distance in millimetres — snapped to the nearest vertex, edge midpoint or face centre. Click near a hole and the diameter comes back as a circle rather than a chord. The section slider cuts the model along X, Y or Z so you can inspect internal geometry and read wall thickness where it matters.
Export when the numbers are right
Once you know what the file holds, convert it to OBJ for modelling, 3MF for a slicer that reads units and colour, GLB for the web, or PLY for research tools. The download arrives with the same triangle count and bounding box — nothing is simplified or re-meshed unless you chose a target that cannot carry the original data.
Technical specifications
| Reads | .stl — binary and ASCII |
|---|---|
| Measures | Distance, angle, wall thickness, hole diameter |
| Sections | X / Y / Z cutting plane with adjustable position |
| Rendering | Shaded, wireframe, and edge overlay at 25° |
| Converts to | .obj, .3mf, .glb, .gltf, .ply, .usdz |
| Runs in | Browser — no install, no upload, no account |
Frequently asked questions
Can this editor modify the geometry of an STL?
Not in the way a modelling tool does. It measures, sections and converts; it does not move vertices, perform booleans or remesh. If you need to edit the actual triangles — fill holes, cut away a support, or reshape a surface — you need Blender, Meshmixer or FreeCAD. What this page does is the step before and after that: inspecting the file to decide what needs changing, and converting the result for the next tool in the chain.
How accurate is the measurement?
The measurement snaps to features the mesh actually stores — vertices, edge midpoints and face centres — so it is as accurate as the tessellation. On a flat face or a straight edge that is exact. On a curve it depends on how many triangles approximate it: a coarse cylinder reports a chord across a facet rather than the true arc. The error is visible before you click, because the snap point tracks the feature it locked onto.
What does the section plane show?
A cut through the mesh along the axis you pick — X, Y or Z — at a position you drag with a slider. The solid half is drawn normally; the removed half disappears. This is the fastest way to check wall thickness, find internal voids or confirm that a part is truly hollow before printing. The cut is visual only; it does not alter the file.
Why does the panel say the mesh is not watertight?
Because it has edges shared by only one triangle, which means the surface is open somewhere. An STL slicer needs a closed shell to decide what is inside and what is outside, so the watertight row is the first thing to check before sending a file to a printer. The count of free edges tells you how large the problem is — a few usually mean a small gap, hundreds usually mean the export dropped one side of the model.
Is there a file-size limit?
No hard limit. The file is parsed in your browser's memory, so the practical ceiling is whatever your machine can hold. A 200 MB binary STL is around 4 million triangles and loads in a few seconds on most hardware. Beyond that, loading slows and the tab may run out of memory — but nothing is refused or truncated, because there is no server to enforce a cap.
What is the difference between this and the STL Viewer?
They run the same tool. This page foregrounds the editing workflow — measure first, then decide whether to convert — and answers the questions someone searching for an STL editor is likely asking. The viewer page leads with opening and inspecting. Both have every feature; neither hides anything behind a paywall or a second upload.
About editing an STL and what that actually means
Most people searching for an STL editor want one of two things: a way to inspect the mesh before printing, or a way to get it into another format for a tool that can do real geometry editing. This page handles both. The measurement and section tools answer the inspection questions — is this wall thick enough, does this hole have the right diameter, is the mesh closed — and the converter handles the format step. What it deliberately does not do is modify triangles, because that job belongs to a mesh editor with undo, selection and booleans, not a web page.
The file never leaves your machine. The parser, the measurer and the exporter all run in the browser tab — there is no upload queue, no processing server and no reason the page would need to know what you are working on. That also means there is no size cap enforced by a backend: whatever your browser can allocate, this page will try to open.
If what you actually need is full geometry editing — converting the mesh to a STEP solid is the path that gets you there with real surfaces rather than triangles, and converting to OBJ is the one that opens the file in Blender or any DCC package.
Where your file is processed
Every number on this page is worked out by JavaScript running in the tab you are reading it in. The model you open is read straight off your own disk — it is never uploaded, logged or kept, which is also why these tools carry on working after you disconnect from the network.
One clause specific to this page: engineering files often contain proprietary geometry. Nothing about your STL — its triangles, its measurements, its name — is transmitted or stored, because there is no server here to transmit it to.