Di Huy Nguyen · ·
PLY is what comes out of 3D scanners, photogrammetry software and mesh research tools. STL is what slicers and printing services ask for. That mismatch is why this conversion exists, and almost everyone doing it is trying to print or quote a scan.
The two formats are closer than they look: both store a plain triangle mesh and neither records a unit of measurement. The difference that matters is that PLY can carry a colour on every vertex, and STL cannot carry colour at all. There is also one case where the conversion is simply impossible, and it is a common one with scan data.
We built three PLY files today, pushed them through the same converter this page uses, and re-opened every result in Blender 5.1 to count what arrived. The numbers below are those measurements.
What the test conversions kept and lost
The mesh input was a scan-shaped blob with 162 vertices, 320 triangles, a green-to-red colour on every vertex and no materials, written once as a binary PLY (7.0 KB) and once as an ASCII PLY (11.8 KB). The third file was a point cloud: 2,000 coloured points and no faces at all, 32.2 KB. Each conversion finished in about two seconds.
| Input | Result | Kept | Lost |
|---|---|---|---|
| Binary PLY mesh | 16.1 KB binary STL, 320 triangles | Every triangle, and the exact coordinates: 0.150 by 0.150 by 0.045 | The per-vertex colour, with nothing in STL able to hold it |
| ASCII PLY mesh | 16.1 KB binary STL, 320 triangles | Identical to the binary result, down to the byte count | The same per-vertex colour |
| Point-cloud PLY | No file. The conversion was refused with an explanation | Nothing, by design | Nothing was lost either, because nothing was produced |
If your PLY is a point cloud, STL is not an option
This is the single most useful thing to know about this conversion. Plenty of scanners and photogrammetry tools export a PLY that lists points and no faces at all. STL is a list of triangles, so there is nothing to write: a point cloud cannot be expressed in it.
Our 2,000-point test file was refused before any file was produced, with a message naming the point count and suggesting what to do instead, rather than silently handing back an empty STL. If you see that message, your file is a cloud, and no converter anywhere can turn it into a printable mesh on its own.
There are two honest ways forward. If you only need the points somewhere else, convert to OBJ instead, which this site does offer from PLY: we tested it and all 2,000 points came through as point entries, although the per-point colour did not. If you need a printable surface, you have to reconstruct one first, in MeshLab or CloudCompare, using Poisson surface reconstruction or a similar method. That is a modelling decision with real parameters, which is exactly why no converter makes it for you.
Colour is the thing you lose, and it does not come back
Our source PLY declared red, green, blue and alpha on every vertex, running from green at the bottom of the object to red at the top. The STL came back with no colour information whatsoever, because the format has no field for it.
We also checked the return trip: converting that STL back to PLY produced a 6.3 KB file whose header lists only x, y and z. The colour is not hidden or dimmed, it is gone. Keep the original PLY if the colour matters and treat the STL as the printing copy.
For colour printing, STL is the wrong target in the first place. A format that stores colour per object or per material, such as 3MF, is what colour-capable slicers expect, and the colour still has to exist in the file you hand them.
Expect the STL to be larger than the PLY
People are often surprised by this. Our 7.0 KB binary PLY became a 16.1 KB STL, around 2.3 times bigger, for exactly the same 320 triangles.
The reason is how each format stores a mesh. PLY lists every vertex once and then describes faces as indices into that list. Binary STL has no index list: it writes three full vertex positions plus a normal for every single triangle, so a vertex shared by six triangles is stored six times. Our output was 84 bytes of header plus 50 bytes per triangle, which is the binary STL layout exactly.
On a small test file that does not matter. On a real scan of several million triangles it is the difference between a file you can upload and one you cannot, so simplify the mesh before converting if you are anywhere near the limit.
Scale: neither format knows what a unit is
Our scan was authored in metres, as photogrammetry output often is, and measured 0.150 by 0.150 by 0.045. The STL contains those same numbers, unchanged. A slicer reads millimetres, so it sees an object 0.15 mm wide, which is a speck.
That is not a conversion fault. Neither PLY nor STL stores a unit, so the numbers mean whatever the program reading them decides. If your converted scan arrives microscopic, multiply by 1000; if it arrives enormous, divide. Converting the file again will never change this, because there is no unit in either file to correct.
The conversion copies your mesh, it does not repair it
In every test the triangle count out matched the triangle count in: 320 triangles in, 320 triangles out. Nothing was decimated or re-meshed. That is the behaviour you want from a converter, but it also means a scan arrives with all of its original problems.
Scan meshes frequently have holes, self-intersections and flipped normals, and a slicer will complain about exactly those things after the conversion just as it would before. Repair belongs in MeshLab, in Blender, or in the repair function your slicer offers. Converting back and forth will not clean anything up.
Doing the same job on your own machine
- Blender reads and writes both formats: File, Import, PLY, then File, Export, STL. The STL exporter has a scene-unit option, which is the easiest place to deal with a metre-scale scan.
- MeshLab is the better choice for scan work, because it handles huge meshes, has the simplification filters you will want before printing, and does the Poisson reconstruction that turns a point cloud into a surface.
- CloudCompare is built for point clouds specifically, which makes it the right tool when your PLY has no faces and you are not sure what is in it.
- PrusaSlicer, Bambu Studio and most other slicers will import a mesh and export the plate as STL again, so a slicer can double as a converter at the end of the chain.
Limits here, and what happens to your file
- Free: up to 30 MB per file, 10 conversions per hour, 2 running at the same time, no account needed.
- Pro: up to 1 GB per file, 50 conversions per hour, 5 at the same time.
- Uploaded files and their converted results are deleted from the server within 1 hour of upload.
- From a PLY file this site converts to STL, OBJ and GLB. Both binary and ASCII PLY are read, and we confirmed that the two produce the same output.
Tested on 27 October 2026: a 320-triangle scan-shaped mesh with per-vertex colour, exported from Blender 5.1 as both binary PLY (7.0 KB) and ASCII PLY (11.8 KB), plus a points-only PLY of 2,000 coloured points (32.2 KB). All three were converted here, the STL results were re-imported in Blender to count triangles, colour and dimensions, and the point-cloud refusal was recorded exactly as it came back.