Convert STL
to STEP.

Updated 2026-10-19

To convert STL to STEP, drop the .stl into the converter below and download the .step. Where the triangles fit them, planes, cylinders, cones, spheres and tori are rebuilt as true surfaces, so a round hole comes back as one cylindrical face with a radius you can measure, and the result is a closed solid. Where nothing fits, the region stays faceted, and the download says which you got. 2 solid conversions a day need no account. Many converters, FreeCAD's shape-from-mesh among them, give you one flat face per triangle instead.

2 solid-geometry conversions a day with no account. No card, no install. In your browser too: real surfaces, no daily limit, the file never uploaded.

No account needed
Drop a STL file.stl · up to 200 MB

On our servers. No account: deleted within 24 hours. Signed in: kept until you delete them. Never shared or used for training.

ResultSurfaces recovered

Planes, cylinders, cones and spheres are rebuilt as true surfaces where the triangles fit them, and freeform regions as smooth patches, in a closed solid that mates, measures and cuts like modelled geometry. Where they cannot be rebuilt the body is faceted instead, and every conversion says which of the two you got.

The STEP as a faceted converter writes it: 524 flat faces, one per triangle.

One face per triangle · 524 faces. Each hole is a ring of flat strips you cannot select or measure.

The STEP from MeshWeave: 10 faces, 7 planes and 3 cylinders.

MeshWeave · 10 faces: 7 planes and 3 cylinders. The hole measures Ø12.00 mm.

The same 524-triangle STL, converted both ways and coloured one shade per face. A synthetic test part, run through the converter, not drawn.
Box, R3 fillets on every edge, converted to STEP in the browser: 26 faces (6 planar, 12 cylindrical, 8 spherical).

Box, R3 fillets on every edge · 9,452 triangles to 26 faces: 6 planar, 12 cylindrical, 8 spherical. 1.1 s.

Block with a bore and a rim fillet, converted to STEP in the browser: 8 faces (6 planar, 1 cylindrical, 1 toroidal).

Block with a bore and a rim fillet · 8,584 triangles to 8 faces: 6 planar, 1 cylindrical, 1 toroidal. 403 ms.

Cone on a plate, converted to STEP in the browser: 8 faces (7 planar, 1 conical).

Cone on a plate · 1,272 triangles to 8 faces: 7 planar, 1 conical. 125 ms.

Vase, freeform profile, converted to STEP in the browser: 3 faces (2 planar, 1 revolved).

Vase, freeform profile · 9,088 triangles to 3 faces: 2 planar, 1 revolved. 874 ms.

Variable-radius blend, 2 to 6 mm, converted to STEP in the browser: 9 faces (6 planar, 1 cylindrical, 2 freeform).

Variable-radius blend, 2 to 6 mm · 2,602 triangles to 9 faces: 6 planar, 1 cylindrical, 2 freeform. 628 ms.

The plate sample, converted to STEP in the browser: 12 faces (6 planar, 6 cylindrical).

The plate sample · 1,188 triangles to 12 faces: 6 planar, 6 cylindrical. 119 ms.

Converted with In your browser selected on this page, as you would: nothing was uploaded. Each picture is the converter's own preview of the downloaded STEP, one colour per kind of surface: grey planar, red cylindrical, orange conical, blue spherical, green toroidal, magenta revolved, violet freeform. Synthetic test parts and one of the samples on this site. Times are from that drive's machine; yours will differ. Drive of 2026-10-14.

Surfaces are only as accurate as the mesh they come from, and there is no feature history.

ChangesSTL → STEP

What changes between STL and STEP

An STL is a list of triangles: no surfaces, no edges, no unit. A STEP describes a solid with exact surfaces and edges. Wrapping the triangles in a STEP file, one flat face each, is easy, and it is what most converters do: the file opens, but a hole is a ring of slivers nobody can select or dimension.

Here the surfaces are recovered instead. Regions of the mesh that lie on a plane, cylinder, cone, sphere or torus are fitted, and each fit is kept only when every vertex lies close to it. Kept fits become true faces with real lines and circles between them; the figure on this page is one 524-triangle STL converted both ways.

Limits: accuracy follows the mesh, so start from the finest export you have. A sculpted or variable-radius region has no simple surface to find and becomes smooth patches or facets. An STL with gaps may arrive as surfaces rather than a solid. The numbers are read as millimetres, and there is no feature history to recover.

HowThree steps
  1. Drop your .stl file above — up to 200 MB without an account.
  2. STEP is already selected as the output.
  3. Download the .step. Without an account, files are deleted within 24 hours; signed in, they are kept until you delete them.
FormatsWhat you are holding

STL file (stereolithography) (.stl)

STL is the lingua franca of 3D printing: a flat list of triangles. No unit, colour, material or history — a cylinder is a fan of flat strips. The missing unit is the classic cause of scale accidents. Every slicer and mesh tool reads it.

You are printing, meshing or sending to a bureau — where triangles are what is wanted.

STEP file (ISO 10303) (.step / .stp)

STEP (ISO 10303) is the closest thing engineering has to a universal solid format. It stores exact B-rep geometry — a hole is a cylindrical face, not a ring of facets. Fusion 360, Inventor, Onshape, SOLIDWORKS, Creo, NX, CATIA and FreeCAD all read it; .step and .stp are the same format. AP242 supersedes AP203 and AP214.

What you send when the other side has to keep modelling, quote machining, or open the shape in a different CAD system.

Questions11 answered
Is the STEP a real solid, or just triangles in a STEP file?
A real solid. Recognised regions become true planes, cylinders, cones, spheres and tori; only what fits none of them stays faceted.
Why does my STL to STEP from another tool have thousands of faces?
Because it wrapped each triangle in its own flat face. That STEP opens, but nothing round in it can be selected, measured or filleted.
What if my STL is not watertight?
Close it first if you can. A mesh with gaps may come back as open surfaces rather than a closed solid.
What unit is the STEP in?
STL carries no unit, so its numbers are read as millimetres. Scale an inch model before converting.
Is the STL to STEP converter free?
Yes. 2 solid-geometry conversions a day with no account, of 5 in total. A free account converts 4 solid files a day and adds 25 credits. No card. Choose In your browser instead and there is no daily limit at all (the same real surfaces are recovered there, freeform patches included).
Does the STEP result have real curves, or flat facets?
The mesh comes back as a STEP solid with real surfaces: a round hole becomes one cylindrical face. Planes, cylinders, cones and spheres are rebuilt as true surfaces where the triangles fit them, and freeform regions as smooth patches, in a closed solid that mates, measures and cuts like modelled geometry. Where they cannot be rebuilt the body is faceted instead, and every conversion says which of the two you got. Surfaces are only as accurate as the mesh they come from, and there is no feature history.
Will the STEP file open in Fusion 360, Inventor or Onshape?
Yes. STEP is read directly by Fusion 360, Inventor, Onshape, SOLIDWORKS, Creo, NX and FreeCAD. It usually arrives as a solid body with true surfaces, without feature history, and the conversion says when it came back faceted instead.
Can you turn the triangles back into proper CAD surfaces?
Usually. Where the triangles fit them, planes, cylinders, cones and spheres come back as true surfaces, so a hole is one cylindrical face with a radius you can measure, and freeform regions become smooth patches. Where nothing fits, the region stays faceted, and the conversion says which you got. Accuracy follows the mesh, so start from the finest STL you have.
How big a file can I convert?
To a mesh format like STL: 300 MB with a free account, 200 MB without one. To STEP, Parasolid or SLDPRT: 140 MB, because rebuilding a solid takes about twice the memory of writing a mesh. Maker and Studio convert up to 830 MB and 380 MB — a large conversion on a paid plan gets the server to itself.
Is it safe to upload my STL file?
Files travel encrypted and are processed by machine on our own servers — no third parties, no ads or trackers, no AI training. Or skip the upload: choose In your browser above the drop zone and this conversion runs on your own device, so the file never leaves it.
Is my STL file deleted after converting?
Without an account, the upload and the result are deleted within 24 hours. With an account, both stay in your files until you delete them; deleted files leave our servers within 24 hours.
Beyond convertingSame file, four workspaces

Keep the part open: fill it with a lattice, check it with FEA, texture a surface, or slice it into cut-ready sheets. These workspaces are in early access — create an account, then apply from inside the app.

Create free account See pricing

ReadWhy this works the way it does
AlsoOther ways in
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Going the other way? Convert STEP to STL.