Convert STL to SLDPRT

A scanned or downloaded part may arrive as an STL when a SolidWorks workflow requires an editable or archivable .sldprt file. Saving the mesh as an SLDPRT preserves its geometry, but it does not recreate the original parametric feature history.

What the STL format is

STL represents a surface with triangular facets. It is used by 3D scanners, slicers, CAD and modeling applications such as SolidWorks, Fusion 360, Blender, and MeshLab, mainly for additive manufacturing, scanning, prototyping, and mesh exchange.

STL files are normally binary or ASCII and usually contain only triangle geometry. They do not normally include sketches, feature trees, constraints, materials, assemblies, colors, or explicit units. Check a known dimension against the source drawing because an STL does not reliably identify whether its coordinates are millimeters, inches, or another unit.

What the SLDPRT format is

.sldprt is SolidWorks' native part-file format. A native part can contain parametric features, sketches, dimensions, configurations, reference geometry, materials, and an editable feature tree.

An imported STL saved as SLDPRT may instead contain a graphics body, mesh body, surface body, or imported solid. It can be stored, displayed, placed in an assembly, and used for reference, but it is not equivalent to a model built from editable extrudes, revolves, fillets, and sketches.

Convert the STL in SolidWorks

1. Make a copy of the STL, determine its intended units, and repair obvious mesh defects before import.
2. In SolidWorks, select File → Open, change the file type to STL, select the file, and open Options before confirming.
3. Choose the available import type. Use Solid Body for a closed, manageable mesh; Surface Body when triangular surfaces can be repaired and knitted; or Graphics Body when the mesh is for visual reference or is too large for solid conversion. Some releases also provide a mesh-body option.
4. Set the correct unit system, open the file, and verify scale, orientation, known dimensions, holes, gaps, duplicate surfaces, and visible faceting.
5. For a mesh or imported body that only needs to remain in SolidWorks, choose File → Save As, select .sldprt, and save the result.
6. For a parametric model, use the imported object as reference geometry and rebuild the important sketches and features. SolidWorks' ScanTo3D add-in, available in supported editions such as Premium, can help create sections, fit surfaces, knit them, and form a solid; manual remodeling is usually more editable and predictable for mechanical parts.

The available import modes and their performance depend on the SolidWorks release, license, mesh size, and whether the mesh is watertight. A large scan may open only as a graphics body.

Use FreeCAD or an online converter

FreeCAD can provide a desktop intermediary when SolidWorks is unavailable. Import the STL in the Mesh workbench, repair it if necessary, use the Part workbench's Create shape from mesh, convert the resulting closed shape to a solid, and export it as STEP. Open the resulting .step file in SolidWorks, then use File → Save As to create an SLDPRT. The conversion succeeds only when the mesh can produce a valid closed shape, and the result still has no original feature history.

CAD Exchanger Cloud is a reputable online option for converting a nonconfidential STL to STEP, which SolidWorks can then save as SLDPRT. Online services commonly provide STEP or another neutral format rather than a genuinely native SLDPRT. Upload only designs permitted by your security and licensing requirements; use SolidWorks or a local converter for confidential, regulated, or proprietary data.

Quality and compatibility limits

• Tessellation remains visible: curved surfaces in an STL are approximated by triangles. Converting to SLDPRT does not restore mathematically defined arcs or cylinders, and a high-resolution file may create thousands of faces.
• Design intent is lost: software cannot reliably infer the source sketches, constraints, feature order, fillet radii, or modeling decisions from triangles alone.
• Mesh errors can block conversion: holes, inverted normals, self-intersections, duplicate triangles, and non-manifold edges may prevent a valid surface or solid. Repair these defects before import.
• Resolution limits accuracy: increasing the export resolution cannot recover detail absent from the STL. Decimating the mesh can alter dimensions and curved surfaces.
• Verify scale before saving: compare at least one known measurement and apply the required scaling before creating the final part file.
• Preserve a neutral copy: newer SolidWorks releases may create SLDPRT files that older releases cannot open. Save a STEP copy for broader CAD exchange.