# 3D Mesh Converter (STL ↔ OBJ ↔ PLY)

> Convert meshes between STL, OBJ and PLY, ASCII or binary, with unit conversion. Convert an STL, OBJ or PLY mesh to binary or ASCII STL, OBJ, or binary or ASCII PLY. Convert between millimetres, centimetres, metres and inches, and apply an extra uniform scale factor.

Part of usefulweb.app (https://usefulweb.app/). Part of [Renderloom](https://renderloom.usefulweb.app/) (ownerApp: renderloom). Results are deterministic calculations from the inputs and the listed assumptions; the API returns exactly what the web page shows.

## Use it
- Human interface: https://renderloommeshconverter.usefulweb.app/ (interactive tool at https://renderloommeshconverter.usefulweb.app/tool)
- JSON API: POST https://renderloommeshconverter.usefulweb.app/api/v1/calculate with a JSON object of inputs (schema: https://renderloommeshconverter.usefulweb.app/api/v1/tool)
- OpenAPI: https://renderloommeshconverter.usefulweb.app/openapi.json
- MCP (Streamable HTTP): https://renderloommeshconverter.usefulweb.app/mcp - tool `renderloom_mesh_converter`

## Inputs
- file (file): Mesh file (STL, OBJ or PLY) - Binary or ASCII STL, OBJ, or ASCII/binary PLY up to 30 MB and 500000 triangles.
- meshText (textarea): Or paste an ASCII STL, OBJ or PLY mesh
- output (select): Output format
- from (select): Source units
- to (select): Target units
- scale (number): Extra scale factor

## Method
- The source is parsed by the shared mesh engine. STL triangle soups are merged at identical coordinates only, so the geometry is unchanged.
- Coordinates are multiplied by (millimetres per source unit ÷ millimetres per target unit) × the scale factor: 1 in = 25.4 mm, 1 cm = 10 mm, 1 m = 1000 mm.
- Binary STL writes an 80-byte header that never starts with “solid”, a little-endian triangle count and per-triangle normals computed from the winding. OBJ keeps o/g group names; PLY writes x, y, z as float and faces as uchar/int lists.
- ASCII STL and OBJ write the shortest decimal that reads back to the same 64-bit number. Binary STL, binary PLY and ASCII PLY declare 32-bit float coordinates.

## Limits
- Only triangle geometry is converted. Colours, normals, texture coordinates and materials are not carried over. STL keeps no groups; binary STL and PLY store 32-bit coordinates.