Convert STEP to STL

When to convert STEP to STL

Prepare a STEP part for a slicer or print service that accepts STL. The conversion makes a triangle mesh from supported CAD surfaces.

Set the mesh before you export

An STL cannot hold curves, so every curved face becomes flat triangles. Two settings decide how many. Linear deflection is how far a triangle may sit from the true surface, in millimetres. Angular deflection is how far the surface direction may turn from one triangle to the next, in radians. The defaults here are 0.1 mm and 0.5 rad, and the tool accepts 0.001 to 10 mm and 0.05 to 1 rad. Set them in STEP mesh settings and press Preview tessellation: the preview shows the triangle count before anything is exported.

On the test cylinder, which has a 10 mm radius and is 20 mm tall, requesting 1 mm of linear deflection gave 48 triangles, 0.1 mm gave 124 and 0.01 mm gave 396. The sampled chord error, a measurement at sampled edges and not over the whole surface, fell from 0.29 mm to 0.048 mm to 0.0049 mm. Those runs held angular deflection at 1 rad, not this tool's default of 0.5 rad, so they are not what the default settings give. Your part will differ, so preview it. Both settings are requests to the CAD kernel, not a guaranteed tolerance.

What fits

STEP files up to 25 MiB; the tool also opens IGES and BREP. A mesh over 200,000 triangles or 1,000,000 vertices is refused, and an operation that runs past 45 seconds is stopped. A finer setting on a large part can reach those limits: raise the deflection and preview again. Nothing is uploaded.

What the STL loses

Colour, if the STEP file has any: the STL writer emits none. The parts of an assembly, which are placed at their positions and merged into one mesh. The unit: coordinates are written in millimetres, converted from the unit the STEP file declares, and an STL cannot record that, so choose millimetres when your slicer asks. Choose 3MF as the output format to keep the unit in the file.

Availability and file handling

This page uses the adjustable tessellation preparation tool. Its limits are 25 MiB, 200,000 triangles and 1,000,000 vertices. Worker operations stop after 45 seconds and can be cancelled. Files stay in this browser; there is no hosted fallback. Preparation exports bake scene transforms into mesh positions and check coordinates, dimensions and topology after readback. These checks do not establish manufacturing suitability.

What this implementation exports

• A mesh imported from supported CAD geometry

• Coordinates expressed in millimetres when input units are known

What needs checking

• Rounding can change positions and topology; watertightness is not guaranteed

• Texture images, UV coordinates, animation and rigs are not exported

• The output contains no unit declaration; choose its interpretation in the receiving application

• This writer emits no colour

• Preparation exports bake scene transforms into each mesh instance; original hierarchy and shared instancing are not preserved

• Exact CAD curves, surfaces and native design history are not retained

• Point geometry is unsupported by this writer

The CAD reader uses the linear and angular deflection settings selected in the tool. Requested deflection is separate from measured surface error. The example cylinder provides an independent analytic comparison; another model needs its own reference.

Size and units

Check one known dimension after opening the output in its destination application. A one-inch length is 25.4 millimetres; interpreting a coordinate value of 1 as millimetres makes that length 25.4 times smaller. Assigning units to a unitless file requires a known reference or information from its author.

What the test result establishes

The recorded core matrix checked this pair against 44 sample files on 2026-09-07. Those fixture results do not guarantee success for every file, prove manufacturing suitability, or establish a public route. Output readback failures must remain visible; a file being parseable does not prove equivalent geometry.

Keep the source

Keep the original STEP file. Exporting it as STL does not make the process reversible: a later conversion cannot recover information omitted by a reader or writer. For an existing model, compare dimensions, components and any required colours before replacing a working file.