Guide to using OpenCAD · Sean Kim
Free Online STEP & STP Viewer: Open and Measure Files
If a STEP file does not open or the view looks blank, check the format, camera, part visibility and parser results separately. Start with the public sample to confirm that 3D rendering works in your browser.
STP vs STEP, measurements and section views
STP and STEP are extensions used for the same STEP format. Check export settings and units in the source CAD system rather than renaming the file. Select a part, then use distance or diameter measurements and section views to inspect the area of interest.
PMI dimensions saved in the file are separate from measurements made on geometry in the viewer. Volume and mass are computed by integrating over the B-rep surfaces, but distances to B-spline faces and interference checks are approximations computed from the display triangles.
OpenCAD reads .stp·.step·.p21 files in STEP Part 21 format. It covers the B-rep shape, assembly, color and units of AP203·AP214·AP242, but not all objects are displayed exactly as the original.
It also supports gzip (.stp.gz·.stpZ) and ZIP containing STEP files. STEP-XML (.stpx) is not supported. Just changing the extension of the file name does not convert the internal format.
Open the example model and the actual file, one after the other.
JavaScript and WebGL2 must be enabled in your browser. "View Examples" opens a small, pre-built assembly model directly in your browser—no need to select any personal files.
- Verify that mouse-based rotation and zooming work within the example model.
- Click "Open," or drag and drop a STEP file into the window. If it is a compressed file, please wait for the extraction and analysis to complete.
- Check the part count, units, and warnings in the product tree and information panel on the right.
- Opening a different model will replace the current document. You can stop the loading of large files by clicking "Cancel" or pressing the Esc key.
When a file is opened but the screen appears empty
First, select "View All" or press 'F' to ensure the model is fully visible within the screen. Select parts from the product tree, review them via "View Selected Parts," and check for any hidden components or layers.
If cross-section view is enabled, disable it to make comparisons. You can also switch viewing modes—such as wireframe—to determine whether the geometry consists only of lines or includes surfaces.
Compare the warnings in the Information panel with the original CAD display. If the samples look fine but geometry is missing from a particular file, the viewer may not have been able to read that file's geometry or entities.
If it still fails to open, please report the error and provide a minimal example.
Providing details such as the file format, your browser, any errors or warnings displayed, and whether the model appears correctly in the original software can help in reproducing the issue. For public issues, please use a minimal, shareable example—such as a simple shape you’ve created yourself—rather than a proprietary model from a client.
The file is read and drawn in this browser. It is a viewer for looking at geometry and measuring distances, so it cannot edit or re-save STEP files.
