STL to STEP converters compared: facets or true surfaces.

Checked 2026-10-01 against each tool's own pages

A STEP made from an STL is either one flat face per triangle, so a hole arrives as hundreds of slivers, or rebuilt surfaces. MeshWeave rebuilds planes, cylinders, cones, spheres and tori as true surfaces; AnyConv says its output stays faceted, FreeCAD keeps the triangles, and the others checked do not say.

The differenceSame file, two results

The STEP as a faceted converter writes it: 524 flat faces, one per triangle. — The same 524-triangle STL, converted both ways and coloured one shade per face. A synthetic test part, run through the converter, not drawn.

The STEP from MeshWeave: 10 faces, 7 planes and 3 cylinders. — The same 524-triangle STL, converted both ways and coloured one shade per face. A synthetic test part, run through the converter, not drawn.

Side by side5 options

Option	What the STEP is made of	Cost	Account	Where your file goes	Good at	The catch
MeshWeavemeshweave.app/guides/stl-to-step-true-surfaces meshweave.app/privacy	True surfaces: planes, cylinders, cones, spheres, tori, B-spline patches	Free, 2 solid conversions a day without an account	No	Our own servers. Without an account, deleted within 24 hours; never shared or used to train AI.	A round hole comes back as one cylinder you can measure and mate to; the solid is watertight.	No feature tree, and radii are as exact as the mesh was (true of any mesh source).
AnyConvanyconv.com anyconv.com	Faceted: its page says the STEP still comes from a faceted mesh	Free	No	Its servers (Germany, Finland); deleted usually within 1 hour, per its policy	Free, simple, honest about what it returns, 100 MB files.	Curved faces stay as many flat triangles.
FreeCADwiki.freecad.org wiki.freecad.org	Faceted: "shape from mesh" keeps the triangles; Refine Shape then merges only flat regions	Free, open source	No	Your computer	Local and free, and a full modeller to keep working in afterwards.	Several manual steps, and holes and fillets are not rebuilt as cylinders.
ImageToStlimagetostl.com imagetostl.com	Not stated	Free	No	Its servers (UK, US); files kept 4 hours, per its policy	500 MB files and batches of 200, free, plus image-to-3D tools.	What the STEP is made of is not stated.
Convert3Dconvert3d.org	Not stated	Free	No	In your browser, per the site: files are not uploaded	Runs on your own machine, with a very wide format list.	What the STEP is made of is not stated.

"Not stated" means the tool's own pages did not say, on 2026-10-01. If you run one of these tools and something here is wrong or out of date, write to hello@meshweave.app and it will be corrected.