Which STL-to-STEP route should you choose: free, per use, or a person?

Turning triangles back into surfaces is reconstruction, and it is sold three ways: as a free open-source project, as credit spent per conversion, or as an engineer’s time. This page puts the three on one table with the price each one publishes, the deliverable each one returns, and who carries the error. Every figure is either quoted with its source and date or re-run by the test suite; none of them is an estimate.

The short answer

The cheapest route is the free, open-source project; the most expensive is a person. A project released as 2STEP-Converter v2.0.0 on 13 May 2026 converts five mesh inputs into an editable STEP at no charge. A browser tool whose author posted on 10 October 2026 sells the same job as credit: $5 buys about six conversions, roughly $0.83 each. A US reconstruction service captured on 24 September 2020 priced the work at as low as $150 a file, delivered in under a day. All three return a STEP; only the third is a person redrawing the part. The one published accuracy figure that comes with the middle route is 0.033 mm average deviation — the tool author’s own measurement on his own part, not this site’s.

One line about this site, before the table. The converter on the front page runs entirely inside your tab: the file is not uploaded and nothing is stored. It reads STEP and IGES and writes STL — one direction only. It will not take an STL as input, so it is not a fourth route, and nothing on this page should be read as an offer to convert the other way. The two doubts that decide most of these purchases — paying before seeing a result, and handing the file to someone else — are answered by the table’s price column and its last column.

The three routes, at the price each one publishes

The table is the whole page in one place, and its last column is the one people ask about most. A request for a self-hosted version was the most upvoted reply (7 votes) in the October 2026 thread, and another reply (2 votes) says the writer is building one himself. Of the three routes, only the free project can satisfy that request outright: the paid browser tool’s author said he would not ship a self-hosted build, and an outsourced rebuild is by definition a file handed to someone else. That column is also where this site would sit if it did the reverse direction — local, nothing uploaded — which it does not. The direction it does run is the opposite one, and the tab never sends the file anywhere.

What a real result looks like

The middle route has one published number, and it is worth reading carefully. Its author posted a conversion whose average deviation is 0.033 mm, and in the same thread described the output as a fitted surface, not metrology — a smooth NURBS reconstruction that a CAD package will open, not a measurement report. An average is not a worst case: a nominal dimension can move further than the average suggests, so the dimensions you actually cut to still need checking. The rebuild page works through what that mean value hides and why the result is a starting point rather than a certificate.

That is also the honest ceiling of the whole category. The author states that the tool does not replace proper reverse engineering and will not return design intent or a feature tree. No price buys those back from a mesh, because they were never stored in it. If you need a feature tree, you are on the third route or on your own CAD seat, and that is a statement about the file, not about any vendor.

The two objections people actually raised

In the same October 2026 discussion, two replies with votes attached name the doubts that make a buyer hesitate. Neither is about geometry; both are about trust, and they apply to any route you pick.

• “Paid, but no real result shown” (5 votes). The reply asks to see actual conversions before paying. The answer is procedural: ask for one measured pair on a part you know before you spend anything. The only published figure on the middle route is the 0.033 mm average above; a vendor who will not show even one before-and-after is asking you to buy a result you have not seen.
• “I would rather not hand my file over” (7 votes for a self-hosted version, 2 votes for building one). This is the strongest signal in the thread, and it maps straight onto the last column of the table. The paid tool declined to ship a self-hosted build; the outsourced route cannot be local by definition; the free project is the one route that answers the request. If keeping the file is the priority, that narrows the list to one.

This site is on the local side of that argument, with a caveat that has to be said in the same breath: it is local because the kernel runs in the tab, and it runs STEP to STL. It is evidence that local processing is possible, not an offer to do the reverse conversion.

What “local” means here, measured

The front page fetches the OpenCASCADE kernel as a 7,604,031-byte WebAssembly file from this site’s own folder, once per session, and runs it in a worker inside the tab. Nothing about your model leaves the machine, and the upload-safety page gives a one-minute network-panel check that verifies this rather than taking it on trust. The measurements are re-run by the test suite: the flat 10 mm cube is 12 triangles and 684 bytes at every quality setting, and an 18-part assembly of 433,606 bytes comes back as 7,372 triangles in a 368,684-byte STL at Normal. Those numbers describe the forward direction only; the reverse direction is not run here, at any price.

Which route to pick

1. A slicer or a viewer is the destination. No conversion is needed. The STL is the format those tools read; the reverse-direction page explains why the mesh is a delivery format rather than a lost STEP.
2. You need to edit the geometry and you can run software. Start with the free open-source route, then check one known dimension against the fit. It is the only route that costs nothing and the only one you can keep on your own machine.
3. You need a usable STEP and will not learn a kernel. The per-conversion credit is the cheapest paid option at roughly $0.83 a job, and the deliverable is a fitted surface. Budget for checking the dimensions that matter.
4. You need design intent, a feature tree, or a dimension you will cut metal to. Rebuild in CAD or outsource it. The outsourced-rebuild page owns the price history of that route and warns that the 2020 quote is dated, not current.
5. Never pay before one measured result on your own part. That is the 5-vote objection answered, and it applies to every route above, including the free one.

Questions this page answers

What is the cheapest route from an STL to a STEP file?

A free, open-source route already exists. A project released as 2STEP-Converter v2.0.0 on 13 May 2026 reads five mesh inputs and writes an editable STEP at no charge. The middle route is a browser tool that sells credit rather than a licence: its author posted on 10 October 2026 that a new account gets $5 of credit, about six conversions, which works out at roughly $0.83 each. The most expensive route is a person: a US reconstruction service captured on 24 September 2020 opened its price list at as low as $150 a file.

Can I trust the dimensions a mesh-to-CAD tool returns?

Not as metrology. The author of one browser-based tool describes his own output as a fitted surface rather than a measurement, and the one published figure in the thread is 0.033 mm average deviation on a particular part. An average hides the individual dimensions that moved furthest, which is why the rebuild page treats the result as a starting point and recommends checking the dimensions you actually need before cutting metal. The tool itself does not claim to replace reverse engineering or to return design intent.

Is there a route that keeps my model off someone else's server?

Only the free, open-source route can genuinely run on hardware you control. A request for a self-hosted version was the most upvoted reply in the October 2026 thread, and the paid tool's author declined to ship one, saying that managing a single app is easier than managing many operating systems. The outsourced route is defined by sending the file to an engineer, so it cannot be local. This site's own converter is local and uploads nothing, but it runs STEP to STL, the opposite direction, and it will not accept an STL as input.

Does this site convert an STL into a STEP file?

No. The converter here reads STEP and IGES files and writes STL, one direction only. It will not take an STL as input, it sells no reconstruction, and no route described on this page is offered here. The page compares routes that other people publish so that the price and the deliverable of each one can be read in the same place; the format list this site accepts belongs to the verification page and is not repeated here.

Where these numbers come from

• 2STEP-Converter v2.0.0, five mesh inputs, free and open source, 13 May 2026 — the release thread recorded in this project’s ammo list under thread identifier t3_1tbj4np (r/3Dprinting). That release lists its five inputs as STL, 3MF, OBJ, AMF and IGES and writes an editable STEP; the list is the project’s own claim, quoted about that project, and is not a statement about what this site accepts.
• $5 of credit ≈ 6 conversions ≈ $0.83 each, 0.033 mm average deviation, “a fitted surface, not metrology” — the tool author’s posts on 10 October 2026 in thread t3_1x2ooni (r/3DPrintingTools), recorded in the ammo list with the user name and date. The per-conversion figure is the site’s arithmetic on the author’s two published numbers, not a second price list. The 0.033 mm is somebody else’s measurement, and this page does not adopt it as its own.
• 7 votes for a self-hosted version, 5 votes asking for actual results, 2 votes for building one — vote counts as recorded when the thread family was read on 19 October 2026, kept in the ammo list with the thread identifiers. Vote counts move; the page prints the ones on file.
• “As low as $150 / file”, delivered in under a day, 24 September 2020 — a Wayback Machine capture of stl2step.com, run by 3DChimera. The outsourced-rebuild page owns that quote and its limits: it is a 2020 price for one file, not a current market price.
• 7,604,031 bytes, 12 triangles / 684 bytes, 433,606 bytes → 7,372 triangles → 368,684 bytes — the kernel file’s length on disk and this project’s own measured conversions, re-run by npm test on every release. They describe the forward direction only.
• What this page does not print — no monthly search volume, no keyword bid, no current price for any route, and no claim that any of the three routes is available here. The only prices are the ones each route published, each with its date. The verification page owns the format rejection list; this page links to it rather than repeating it.

npm test

The command above re-runs every number this project measured. The reverse-direction page owns whether STL to STEP is a conversion at all; the rebuild page owns the method; the outsourced-rebuild page owns the 2020 price; the upload-safety page owns the network check; and the converter is where a STEP file meets the kernel, for free, in the tab.