STEP vs STP vs STL: file differences and viewer units

If a supplier sends both STEP and STL, decide what you need to inspect first. Assembly layout and an exported printing mesh call for different source information and review checks.

What to ask when requesting a model
File	Data and browser display	Ask the author
STEP · STP	Extensions used for the same STEP family. TotalViewer converts supported geometry into a display mesh.	Included parts, source units and revision
STL	A triangle mesh. It does not preserve the original CAD part and surface semantics in the same way.	Actual coordinate units and mesh export detail
OBJ · PLY	Supported polygon meshes. External OBJ materials and PLY point clouds are not supported.	Whether the needed geometry is inside the file and which units apply

Does renaming STP to STEP convert the model?

STEP and STP are extensions used for the same format family, and both can be selected in TotalViewer. Contents and export settings still affect compatibility. Renaming an STL to STEP does not reconstruct CAD geometry.

Check units before interpreting a measurement

Ask the author for the original CAD units and one known reference dimension.
Check the millimetre-based STEP or IGES conversion. STL, OBJ and PLY data without unit information uses model-coordinate units.
If using Pro measurement, compare its approximate mesh value with the reference. Use the original CAD for tolerance decisions.
If units disagree, ask for a new export with verified source units and export settings.

Missing parts or a conversion that will not finish

CAD sources are limited to 8 MiB and meshes to 16 MiB. Display limits are 100,000 triangles, 300,000 vertices and 128 parts. STEP, IGES and BREP conversion also has 128 MiB memory, 25-second and 16 MiB display-output limits.

Detailed surfaces and assemblies can generate complex meshes from small files. Request just the required parts. Pro removes the daily open count limit, not these geometry, compatibility or device limits.

Record a review that another person can follow

Record the filename, revision, source units, inspected parts and missing-geometry warnings. Check PMI, precise surfaces and manufacturing dimensions in the source CAD or an author-supplied reference drawing.

Open the relevant viewer or workflow

STEP viewer and synthetic sample →STL, OBJ and PLY scope →Try synthetic 3D review tools →

Basic viewing: one file per day in the same browser, without signup. File, geometry and device limits apply to Free and Pro. Pro checkout is being prepared. The viewer and interactive demo interface is currently Korean.