PMX to STEP Converter
FileFlip converts PMX to STEP entirely inside your browser, using Assimp compiled to WebAssembly. The file is never uploaded to a server: it is read off your disk, converted on your own machine, and saved back by the browser. That means no file-size limit, no queue and no account.
How do I convert a PMX file to STEP?#
- Drop your PMX file onto the converter at the top of this page, or click it to pick one from your computer. You can add as many as you like.
- Leave the target set to STEP and the conversion starts on its own. FileFlip downloads 11.2 MB of WebAssembly the first time and nothing after that, then runs Assimp on your own machine.
- Save the STEP file. Your browser writes it straight to your downloads folder, because there was never a server holding it.
Does converting PMX to STEP lose quality?#
Not in the sense of pixels or samples. Converting PMX to STEP rebuilds the file in STEP's own model rather than re-encoding it, so everything STEP can represent comes through exactly and anything it cannot has to be dropped. Expect the geometry to be exact, and anything the target has no place for, such as a rig, to be left behind.
Is it safe to convert PMX files online?#
Yes, because nothing is uploaded. FileFlip converts PMX files inside the browser tab you already have open, using WebAssembly builds of the same engines a desktop converter would install. Your file is read from your own disk into the page's memory, and no request carrying it is ever made.
You do not have to take that on trust. Open your browser's network panel, run a conversion, and you will see the engine come down and your file go nowhere. There is no upload, no server-side copy, no retention window, and no account tied to what you converted.
How FileFlip works lists every engine, its version and its download size, and shows how to check for yourself that nothing leaves your machine.
What PMX to STEP actually does to the file#
Converting PMX to STEP runs on Assimp, downloads 11.2 MB of WebAssembly the first time and nothing after that, rebuilds the file in the target's own model, and drops skeleton and animation.
| Engine | Assimp |
|---|---|
| Conversion path | One step: PMX → STEP |
| Downloaded to your browser | 11.2 MB, once, then cached by your browser |
| Quality | Rebuilt in the target's model |
| You get back | One file |
| Where it runs | In a background worker, so the page stays responsive |
What survives the conversion
| What is in the file | This conversion | Why |
|---|---|---|
| Materials | Sometimes | Survives for some files and not others. |
| Textures | Sometimes | Survives for some files and not others. |
| Skeleton and animation | Dropped | The target format has nowhere to put it. |
Worth knowing before you start:
- if the source carries a skeleton or animation, this target has no place to store it
What is a PMX file?#
A PMX file is a binary character model for MikuMikuDance, the successor to the older PMD format, built by Yu Higuchi's tools to hold a mesh alongside its bones, facial morphs and rigid-body physics as one package that MMD loads and animates directly.
Use PMX when a character needs to be posed, animated or physics-simulated inside MikuMikuDance or the wider MMD tool ecosystem.
Convert PMX to glTF or FBX when an MMD character needs to move into a game engine or renderer outside the MMD ecosystem.
What is an STEP file?#
An STP file holds a STEP product model in ISO 10303's plain-text exchange syntax, encoding exact boundary-representation solids, surfaces and curves rather than a triangulated mesh.
Use STEP whenever exact CAD geometry, not an approximated mesh, needs to move between two different CAD systems.
Convert a STEP file to a mesh format like STL or OBJ once the model is finished and only needs to be viewed, rendered or 3D printed rather than edited as a solid.
PMX to STEP questions people ask#
What is a PMX file?
A PMX file is a MikuMikuDance character model, storing a mesh together with its bones, facial morphs and rigid-body physics in one binary file. It's the successor to the older PMD format and the format almost all current MMD character content is distributed in.
What's the difference between PMD and PMX?
PMD is the older MikuMikuDance model format, and PMX succeeded it with a more flexible bone and morph system, support for more materials, and additional physics options. PMX Editor can open and convert PMD files, and current MMD content is essentially all PMX now.
Can I open a PMX file outside MikuMikuDance?
Yes, Blender opens PMX files through the community mmd_tools add-on, which reads the mesh, bones, morphs and physics much the way MikuMikuDance does. Outside of MMD-focused tools, native PMX support is rare.
What does STP stand for?
STP is the file extension for STEP, the Standard for the Exchange of Product model data, formally ISO 10303. It's the neutral format mechanical CAD systems use to hand solid models to each other.