3D file converter

Free 3D file converter.

Convert a SOLIDWORKS part (.sldprt), a Parasolid file (.x_t, .x_b), or a STEP, IGES or STL file to STEP, IGES or STL, free and without an account. The conversion runs in your browser, so the file never leaves your computer, and every result is read back and checked against the original before it is offered for download.

Your file never leaves your computer: the conversion runs in your browser.

What converts to what

Six formats in, three out. A solid is written face for face. An IGES file's surfaces are first sewn into a solid, closing gaps of up to 0.1 mm. The one approximation is a mesh, whichever way it goes: an STL made from a solid is a mesh within the resolution you pick, and a STEP or IGES made from an STL is a faceted solid of flat faces made of the mesh's triangles.

Formats the converter reads and writes
FromTo STEPTo IGESTo STL
SOLIDWORKS part (.sldprt), 2015 and laterExact solidExact faces (trimmed surfaces)Mesh, Standard or Fine
Parasolid (.x_t, .x_b)Exact solidExact faces (trimmed surfaces)Mesh, Standard or Fine
STEP (.step, .stp)Already STEPExact faces (trimmed surfaces)Mesh, Standard or Fine
IGES (.igs, .iges)Sewn into a solid first, closing gaps up to 0.1 mmAlready IGESMesh, Standard or Fine
STL (.stl), binary or ASCIIFaceted solidFaceted solidAlready STL

STEP is written as AP214 and IGES as version 5.3 with trimmed surfaces, the forms most CAD and CAM systems read. STL is written as binary. Everything is in millimetres, and the new file takes the original's name with the new extension: bracket.sldprt becomes bracket.step.

Every conversion is checked

After writing the new file, the converter reads it back with the same readers it used on yours and compares what it finds with the part it started from. If any comparison fails there is no download, and the page says why.

  • Solid to STEP or IGES. Same volume and surface area to one part in a million, same bounding box to 0.001 mm, same number of solids.
  • Solid to STL. The mesh's volume and size must stay within what the chosen resolution allows. Standard keeps every triangle within 0.05 mm of the true surface and turns at most 5 degrees from one facet to the next; Fine holds 0.01 mm and 1 degree. That check does not prove the mesh is closed.
  • STL to STEP or IGES. One flat face for every patch of triangles that lie exactly in one plane, often a single triangle, and the same volume and surface area as the mesh to one part in a billion.

The line above the Download button says what was compared and how closely the two files agreed, worked out from the files themselves rather than written in advance.

What is kept, and what is not

  • The geometry, exactly. A solid is written face for face as it was read: planes, cylinders, fillets and freeform surfaces stay what they are. An IGES file's surfaces are first sewn into a solid, closing gaps of up to 0.1 mm.
  • Every body. A multi-body part keeps all its solids. A STEP or IGES assembly is flattened into one file of solids, each where it sat, without the assembly tree.
  • Not the feature tree. A SLDPRT converted to STEP is the finished solid. Its sketches, features and history stay in SOLIDWORKS.
  • Not colours, names or annotations. Geometry only: no appearances, feature names or PMI.
  • An STL stays a mesh. Converted to STEP or IGES it becomes a faceted solid of flat faces, because a mesh cannot be turned back into curved CAD faces exactly. A mesh that does not close becomes surfaces only, labelled as an open mesh, and so does a closed mesh with one loose face anywhere in the file. Closed bodies that touch or cross one another are not made into STEP or IGES at all: where they meet, which side is solid cannot be told.

Limits

  • Files up to 200 MB. Big parts take longer, and the page counts the seconds while it works.
  • SOLIDWORKS parts saved by SOLIDWORKS 2015 or later. Older parts, and assemblies (.sldasm), are refused with the reason and what to do instead.
  • Nothing converts to SLDPRT. Only SOLIDWORKS writes SOLIDWORKS files.
  • STL to STEP or IGES takes meshes of up to 30,000 triangles here. A solid made from a mesh is slow to build in a browser and large, about 1.1 KB of STEP per triangle: 30,000 triangles take about half a minute to STEP and 40 seconds to IGES on a fast desktop, and make a 32 MB STEP. Reduce a bigger mesh in your mesh or CAD software first; the page says so before the converter starts.
  • Phones and some tablets give a page less memory than a desktop does, so a large part may need a desktop browser.
  • A part the reader cannot rebuild exactly is refused, with the reason. Nothing is repaired quietly.

Convert a specific pair

SLDPRT to STEPA SOLIDWORKS part as an exact solid any CAD system opens. SLDPRT to STLA mesh for 3D printing, at Standard or Fine resolution. SLDPRT to IGESFor the older CAM and CNC software that still asks for IGES. X_T to STEPA Parasolid file, text or binary, as STEP. STEP to IGESThe same faces, rewritten for software that will not take STEP. IGES to STEPLoose surfaces sewn into a solid and written as STEP. STEP to STLAn exact solid turned into a checked mesh. STL to STEPA mesh made into a faceted solid, and labelled as one.

Questions about the converter

Is the converter really free?

Yes. There is no account, no sign-up and no limit on how many files you convert. It can be free because no server does the work: the conversion runs in your browser. Lasertally makes quoting software for laser-cutting shops, and the converter is one way shops find it.

Is my file uploaded anywhere?

No. The file is read and converted inside your browser, by a program that downloads once and then runs on your own computer.

The converter itself sends back only an anonymous count: which formats were converted, whether the check passed, a rough size range, how long it took and which of the converter's pages it ran on. Never the file, its name or anything inside it. The site's usual analytics also run on this page, as on every page of the site.

Does converting SLDPRT to STEP keep the feature tree?

No. STEP carries the exact solid, face for face, but not the sketches, features and history SOLIDWORKS builds it from. Any CAD system can open the STEP, measure it and model on top of it, but cannot edit the original features. Keep the SLDPRT for that.

Why is a STEP file made from an STL faceted?

An STL holds only triangles, with no record of the curved surfaces they were cut from. The converter turns the triangles into the flat faces of a solid (triangles that lie exactly in one plane become one face), which is exact to the mesh but not to the original design. Rebuilding true curved faces from a mesh is a guess, and the converter does not guess.

How do I know the converted file is right?

Every result is read back and compared with what was read from your file before you can download it. For STEP and IGES that is volume, surface area, size and the number of solids. An STL mesh is checked on volume and size only, which does not prove it is closed. The line above the Download button says what was compared and how closely it agreed. A file that fails the check is not offered at all.

Can it convert SOLIDWORKS assemblies?

No. An assembly file (.sldasm) refers to its parts rather than containing them. Open it in SOLIDWORKS and save each part, or save the whole assembly as one STEP file, and convert that.

Credits and licences

The converter is Lasertally's own code, built on these projects:

  • Open CASCADE Technology 7.9.3, the CAD kernel that reads and writes STEP, IGES and STL. GNU LGPL version 2.1 with the Open CASCADE exception (licence).
  • parasolid-core 0.3.7, whose description of the Parasolid format the SOLIDWORKS and Parasolid reader follows. MIT License, and Apache License 2.0 for the readers it adopted (project).
  • sldprt-export, credited for how a SOLIDWORKS part's saved display mesh is laid out. MIT License (project).
  • The cadmpeg notes on the SOLIDWORKS file format, which the reader's handling of the part file's blocks follows. Creative Commons Attribution 4.0 (licence).
  • zlib, for the compressed streams inside SOLIDWORKS files. zlib License.
  • Emscripten, which compiles all of it to WebAssembly for your browser. MIT and University of Illinois/NCSA licences.
  • Source and relinking. Open CASCADE Technology runs as its own file, with two small changes needed to build it for WebAssembly. SOURCE.txt gives its source, both changes in full, how it was built, how to run the converter on your own build of it, the licences of everything in the converter's files, and our written offer of the source.

Quoting laser-cut parts from files like these?

Lasertally is Windows software for fabrication shops. It opens STEP, IGES, DXF and NC1 files, measures the pierces, cut length and bends off the geometry, and prices the part on your own rate card.

Start your free month Quoting from STEP

Keep reading

STEP file quotingWhat Lasertally reads out of a STEP file once you have one. DXF to quoteThe flat-profile route, and when a DXF is the right thing to send. QuotingPre-quote checks, rate cards and how the engine is calibrated to the cent.