Free under 5 MBSTL → BREPNo software installation

Convert STL to BREP online

Convert an STL (.stl) triangle mesh to BREP (.brep or .brp) for Open CASCADE and topology-based CAD workflows. The result can carry faces, edges and vertices derived from the mesh, but it does not recover smooth analytic surfaces, sketches or feature history.

Encrypted uploads Files up to 300 MB Automatically deleted within 7 days

Upload your STL file

Choose one STL file. This page is already configured to create BREP output.

Secure

Drag and drop your STL file here

or choose a file from your computer

Browse files

Maximum file size: 300 MB

Files under 5 MB convert and download free. Larger files use one credit for one completed download, regardless of file size.

No STL file available? Try a STL sample to see the workflow.

Pricing

Pay as you go, cheaper by the pack

Files under 5 MB convert and download free. Larger files use one credit for one completed download, regardless of file size. 1 credit downloads any file, any size, and credits never expire.

Starter

3credits

$7.99

$2.66 each

Save 11%

3 downloads of any size. Good for a one-off project.

Pro

5credits

$12.99

$2.60 each

Save 13%

5 downloads of any size. The everyday choice.

★ Most popular

Team

10credits

$19.99

$2.00 each

Save 33%

10 downloads of any size. Best balance of price and volume.

Studio

15credits

$26.99

$1.80 each

Save 40% · best value

15 downloads of any size. Lowest price per file.

Just need one? Pay $2.99 for a single downloadNo subscriptionCredits never expireInvoice on every purchase

No desktop software

Start the STL-to-BREP workflow in your browser without installing a CAD application or plugin.

Mesh-derived boundary representation

The BREP output reflects the STL facets. A watertight mesh may form a closed shell or solid; damaged meshes may remain open or invalid.

Ready to inspect

Open the BREP result in an Open CASCADE-compatible viewer or CAD system and check body status, face count, scale and open edges.

Open BREP viewer

Private file handling

Files stay private, are never added to the public CAD library and are automatically deleted within 7 days.

Continue your CAD workflow

Inspect the STL, verify the BREP or request specialist help

Inspect the STL before conversion, validate the BREP topology afterward, or request a native rebuild when smooth editable geometry matters.

Check the source STLCheck watertightness, normals, disconnected shells, non-manifold edges and triangle density before conversion.Open STL viewerInspect the BREP outputConfirm whether the result is a solid, closed shell, open shell or collection of faceted faces.Open BREP viewerNeed editable manufacturing geometry?Ask a CAD designer to rebuild clean analytic faces and features instead of editing thousands of mesh-derived BREP faces.Hire a CAD designer

Simple conversion workflow

How to convert STL to BREP online

Move from a triangular STL mesh to a BREP topology file in three steps.

01

Upload the STL file

Choose a .stl file up to 300 MB. Watertight, manifold meshes with consistent normals produce the most reliable topology.

02

Convert to BREP

The route is preconfigured for BREP. Start the conversion without searching through a destination-format menu.

03

Download and verify

Open the .brep or .brp result in the target CAD kernel. Verify units, body validity, open edges and face count.

Convert STL to BREP

Format behaviour

What actually happens when STL is converted to BREP?

STL stores an unstructured triangle surface. BREP represents geometry through connected faces, edges and vertices. Conversion creates BREP topology from the STL facets; it may sew a clean watertight mesh into a closed shell or solid, but it does not infer cylinders, fillets, holes or the original feature tree.

What is normally retained

  • Visible shape defined by triangles
  • Vertex and face boundaries
  • Model orientation
  • Separate shells where supported
  • Closed volume when a valid watertight mesh sews successfully

What is not retained or may change

  • Original sketches, dimensions and constraints
  • Parametric features and design history
  • Exact planes, cylinders, cones and NURBS surfaces
  • STL unit intent unless supplied separately
  • Materials, colors and manufacturing metadata
STL meshSTL
BREP solidBREP

Format comparison

STL versus BREP

Choose the format according to what the next application needs—not because one is universally better.

FeatureSTL STLBREP BREP
Data modelTriangle surface meshConnected faces, edges and vertices
Body statusMay be watertight but has no CAD solid topologyCan represent shells or solids when topology is valid
UnitsNo standard unit fieldApplication/kernel dependent; verify dimensions
EditabilityMesh editingTopology editing, often with one face per triangle
Best use3D printing and mesh workflowsOpen CASCADE and B-rep CAD workflows

Choose BREP when

An Open CASCADE workflow specifically needs BREP

You need faces, edges and topology rather than raw triangles

The mesh is clean enough to sew into usable topology

You accept that the model may remain faceted

Keep STL when

The next step is slicing or 3D printing

You are still repairing or simplifying the mesh

A lightweight triangle file is preferred

You need to preserve the original tessellation exactly

Before continuing

Check the converted BREP before using it

A BREP file can be created successfully and still contain open shells or thousands of unusable faces. Validate topology before downstream use.

  1. 01

    Verify scale and intended units

    STL has no standard unit field; measure a known feature after import.

  2. 02

    Confirm body status

    Check whether the result is a valid solid, closed shell, open shell or compound.

  3. 03

    Inspect open and non-manifold edges

    Look for holes, T-junctions, overlaps and self-intersections inherited from the mesh.

  4. 04

    Review face count

    A face-per-triangle result may be too heavy for editing or Boolean operations.

  5. 05

    Check orientation

    Confirm shell and face orientation and recalculate source normals if needed.

  6. 06

    Run the target operation

    Test the Boolean, healing or CAD operation that motivated the conversion.

Common problems

STL-to-BREP troubleshooting

Failures usually trace back to non-manifold STL geometry, missing unit context, invalid normals or excessive triangle density.

The BREP is an open shell

Cause: The STL contains holes or edges that do not sew.

Fix: Repair and close the mesh before converting again.

The result has thousands of faces

Cause: Each triangle was represented as a separate BREP face.

Fix: Decimate non-critical mesh detail or commission a native rebuild.

Boolean operations fail

Cause: The converted topology is invalid, self-intersecting or too fragmented.

Fix: Run mesh repair, then validate and heal the BREP in the target kernel.

The model is the wrong size

Cause: The STL did not declare a physical unit.

Fix: Apply the intended millimetre, inch or other scale after measuring a known feature.

Faces are reversed or missing

Cause: Source normals or triangles are inconsistent.

Fix: Repair invalid facets and recalculate normals before retrying.

The file opens but is hard to edit

Cause: BREP topology does not equal recovered parametric features.

Fix: Use the file for exchange; request a native rebuild for design changes.

Hire a CAD designer

Secure processing

Your design files remain yours

Engineering files can contain confidential geometry and documentation. Marathon OS keeps conversion uploads separate from its public CAD library and explains how each file is handled.

Encrypted transfer

Files are transferred over an encrypted connection.

Automatic deletion

Uploaded source files and converted outputs are automatically deleted within 7 days.

You retain ownership

Uploading or converting a file does not transfer ownership of the design to Marathon OS.

Never published automatically

Conversion files are not listed in the public Marathon OS CAD library.

Use tools that support the same STL-to-BREP workflow.

STL

STL file viewer

inspect the source mesh

BREP

BREP file viewer

check the converted topology

STLSTEP

STL to STEP

create a STEP-compatible result

BREPSTL

BREP to STL

return to a printable mesh

OBJBREP

OBJ to BREP

convert another mesh format

CAD

Hire a CAD designer

rebuild clean native geometry

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STEPSTL

STEP to STL

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Frequently asked questions

Frequently asked questions about STL to BREP conversion

Clear answers about output behavior, compatibility, pricing, file limits and privacy.

  • How do I convert STL to BREP online?

    Upload STL (.stl), confirm BREP as the preselected output, convert and download BREP (.brep, .brp). Verify the result in the target application.

  • Why convert STL to BREP?

    Use BREP when an Open CASCADE or topology-based CAD workflow requires connected faces, edges and vertices rather than a raw triangle mesh.

  • Will STL to BREP create a smooth, editable solid?

    Not automatically. A clean STL may become a valid closed BREP, but the faces are still derived from triangles and no original parametric features are recovered.

  • Which STL and BREP extensions are supported?

    This route accepts .stl input and creates .brep, .brp output.

  • Is the STL to BREP converter free?

    Files under 5 MB can be converted and downloaded free. Larger files use one credit for one completed download.

  • What is the maximum STL file size?

    You can upload a STL file up to 300 MB. Very dense meshes can create enormous BREP face counts and slow or fail downstream operations.

  • How are my files handled?

    Files are transferred securely, are not published to the public CAD library and are automatically deleted within 7 days. You retain ownership.

Need more than a faceted BREP?

A file-format change does not reverse-engineer the original part. Work with a CAD designer when you need analytic surfaces, tolerances, features or a production-ready native model.

Hire a CAD designerConvert another STL file