Tác giả: Huy Nguyen · ·
STL and PLY both describe a plain triangle mesh, so this conversion is one of the gentler ones on the site. Nothing has to be tessellated, flattened or thrown away. What changes is the packaging, and in one respect the packaging matters a lot.
People go this way for fairly specific reasons: to open a printable part in MeshLab or CloudCompare, to line a printed part up against a scan, to feed mesh-processing or research code that ships a PLY reader and not much else, or simply to get a smaller, properly indexed file to work with.
We converted a real STL through the same pipeline this page uses, read the output header byte by byte, and re-imported the result in Blender 5.1. Here is what actually came out.
Why anyone converts an STL to PLY
- MeshLab, CloudCompare and much of the academic geometry-processing world treat PLY as a first-class format, and some of those tools read it more happily than STL.
- PLY stores a vertex list with faces as indices, which is the shape most mesh algorithms want before they will do anything useful.
- It is the format to be in if you later want per-vertex colour, for example to bake a scan colour onto a printed part or to visualise a deviation map.
- It is simply smaller. Our test file dropped by about 62 percent with no change to the geometry at all.
What the test conversion kept and lost
The input was a binary STL of a machined part, exported from FreeCAD at a 0.1 mm deviation: 1,032 triangles, 51.7 KB, measuring 40 by 20 by 10 mm. The conversion took about two seconds.
| What | In the STL | In the PLY |
|---|---|---|
| Triangles | 1,032 | 1,032 |
| Vertex records | 3,096, three per triangle | 516 unique vertices plus an index list |
| File size | 51,684 bytes | 19,824 bytes, about 62 percent smaller |
| Dimensions | 40 by 20 by 10 | 40 by 20 by 10, unchanged |
| Colour and materials | None, STL cannot store any | None, because there was none to carry |
| Encoding | Binary STL | Binary little-endian PLY with x, y and z only |
The file shrinks because the duplicates go away
A binary STL has no vertex list. It writes three full vertex positions and a face normal for every single triangle, so a corner shared by six triangles is written out six times. Our file was 84 bytes of header plus 50 bytes per triangle, exactly.
PLY works the other way round: a list of unique vertices, then faces that point into it. In our test the 3,096 vertex records in the STL came out as 516 unique vertices, which is the real count for this part, and the file fell to 19,824 bytes.
That tidying up is the practical reason to convert. A mesh whose triangles actually share vertices can be smoothed, decimated, measured and checked for watertightness; a loose pile of unconnected triangles usually cannot, which is why so many tools weld an STL on import anyway.
PLY can hold colour. This conversion will not give you any
This is the expectation worth correcting. PLY is known as the format that stores colour per vertex, so it is natural to assume that converting to it adds that capability. It adds the capability and nothing to put in it.
STL has no colour field at all, so there is nothing to carry across. We measured it both ways: the PLY produced from our STL has only x, y and z in its header, and a separate test that started from a fully coloured PLY, converted it to STL and converted it back produced a 6.3 KB PLY with no colour properties either. Colour that has passed through an STL is gone for good.
If you need a coloured PLY, the colour has to come from the original source — the scan, the photogrammetry project, the textured model — not from an STL. If you want to paint the colour yourself, convert to PLY first and then use the vertex-paint tools in Blender or MeshLab, which is a perfectly normal workflow.
What the output header actually says
The converter writes binary little-endian PLY, which is what you want for anything large: it is compact and fast to load. If a tool in your chain insists on ASCII PLY, the quickest fix is to re-save it from Blender or MeshLab with the ASCII option ticked, rather than hunting for a converter setting here, because there is none.
The header lists only x, y and z per vertex. There are no normals in it, which is worth knowing because the face normals that were in the STL are not carried over as PLY properties. Most tools recompute normals from the triangle winding anyway, so this rarely causes trouble, but if your software shows a flat or inside-out shade, recalculating normals is the first thing to try.
Units stay exactly as they were
Neither format records a unit of measurement, so the numbers simply pass through. Our 40 by 20 by 10 mm part measured 40 by 20 by 10 in the PLY as well.
That is convenient and also a trap: whatever your software assumes one unit to be is what you will see. A part designed in millimetres opens in a metre-based scene as something 40 metres across. Set the import scale once rather than rescaling objects later.
Doing the same job without uploading
- Blender: File, Import, STL, then File, Export, PLY. The export panel is where you choose ASCII instead of binary and whether to include colour attributes and normals.
- MeshLab is the better tool if the mesh is big or if you intend to simplify, clean or colour it afterwards. It imports STL and saves PLY with a checkbox list for exactly which per-vertex properties to write.
- CloudCompare reads both formats too and is the right choice if the next step is comparing the part against scan data.
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 an STL this site also converts to OBJ, GLB, glTF, FBX, 3MF and DAE, so PLY is one of seven targets if you change your mind.
Tested on 27 October 2026: a binary STL of a machined part exported from FreeCAD at 0.1 mm deviation (1,032 triangles, 516 unique points, 51.7 KB, 40 by 20 by 10 mm), converted to PLY here, then re-imported in Blender 5.1 and its PLY header read directly. A second round trip, from a colour-per-vertex PLY to STL and back, was used to check whether colour can return.