What is a .ply file?

What makes PLY different

PLY was written at Stanford to store the output of 3D scanners, including the Stanford Bunny and the Digital Michelangelo Project, and its defining feature is that the header describes the data.

ply
format binary_little_endian 1.0
element vertex 40256
property float x
property float y
property float z
property uchar red
property uchar green
property uchar blue
element face 79821
property list uchar int vertex_indices
end_header

Everything after end_header is exactly what the header said it would be. If a scanner wants to record confidence values, intensity, or a second set of normals, it declares them as extra properties and any conforming reader can skip what it does not understand.

That extensibility is why PLY survived while most academic formats did not.

Colour, without a sidecar file

Unlike OBJ, PLY stores per-vertex colour directly in the file. For scanned objects, where colour varies continuously across the surface instead of coming from a texture map, that is the right model. A coloured scan is one self-contained PLY.

This is the main practical reason to choose PLY over STL: it is the simplest way to move a coloured mesh as a single file.

Point clouds

A PLY may declare vertices and no faces at all. That is a point cloud, the raw output of a laser scanner or photogrammetry step before any surface has been reconstructed.

A point cloud is not a surface. It cannot be sliced, printed, machined or converted to a solid, because there is nothing enclosing anything. Software that pretends otherwise produces an empty file or a mess.

This site detects a face-less PLY and says so, and converting one to STL or STEP produces no geometry rather than a guess. To get a surface from a point cloud you need a reconstruction step: MeshLab's Poisson reconstruction, CloudCompare, or your scanner's own software.

ASCII and binary

Both, declared in the header. ASCII is readable and large. Binary little-endian is what any real scan uses. Big-endian exists and is rare.

Units

PLY has no unit, in common with STL and OBJ. Scanned data is usually in millimetres, and this site assumes millimetres, but nothing in the file says so.

One naming trap that breaks readers

The face list's property is called vertex_indices in the original specification, and vertex_index in a great many files in the wild, including some written by MeshLab and by several scanners. A reader that matches the name exactly opens one and refuses the other, or worse, reads the faces as an unknown property and shows you a point cloud of a perfectly good mesh. This site accepts both spellings. If a PLY you know has faces opens elsewhere as points, this is the first thing to check.

When to use PLY

• 3D scans, especially coloured ones
• Point clouds, where it is the de facto standard alongside E57 and LAS
• Research and pipeline work, where custom per-vertex properties matter

When not to

• Manufacturing: no unit, no exact geometry
• 3D printing: use 3MF or STL, which every slicer prefers
• Web or AR delivery: use GLB or USDZ