What a STEP file holds
STEP is the ISO 10303 standard for exchanging product data, and its first parts were published in 1994. A .step or .stp file is the clear-text encoding from Part 21. It stores exact surfaces and solids (B-rep), so a hole is a true cylinder and a fillet is a true arc. The file also declares its length unit, and an assembly keeps each body separate, often with its own color.
A screen can only draw triangles, so every STEP viewer first tessellates the surfaces. Here OpenCascade, an open-source CAD kernel, does that job in your tab. When the part is a supplier drawing under NDA, it matters that the file never goes to a server.
How the STP file viewer reads units and precision
The viewer reads the unit written in the file and converts it to millimetres. Three test files show how that works.
| test file | declared unit | shown size |
|---|---|---|
| 10 mm cube | mm | 10 mm |
| 1 inch cube | inch | 25.4 mm |
| CAX-IF AS1 assembly from Pro/E | inch (wrong label) | 5080 mm, then 200 × 87 × 150 mm after one switch |
Precision has three steps. On a rounded test cube, Coarse gives 48 triangles, Medium 84 and Fine 172. Pick Coarse for a quick look at a big assembly and Fine before you export a mesh for printing.
Assemblies, colors and the mesh check
Assembly colors come through, so a housing and its fasteners stay easy to tell apart. The Info panel counts the parts and runs the mesh check per body. The AS1 test assembly reports 10 of 10 bodies closed. If one body fails the check, look at it before you print.
The same panel lists the bounding box X × Y × Z in mm or inches, volume in cm³, surface area and weight for 17 materials. Measure snaps to vertices and gives the total distance with ΔX, ΔY and ΔZ. The section plane slides along X, Y or Z and shows the inside in red.
Typical STEP problems and what to do
- The part is 25.4 times too big. Some exporters write millimetre numbers under an inch label. The viewer warns "Check the units"; press "Numbers are millimetres" to get the intended size.
- You have a native CAD file. SLDPRT, IPT and F3D do not open. Export STEP from the program that made the part.
- A huge assembly is slow. Choose Coarse first. Meshes above roughly 1 to 2 million triangles may exhaust the tab's memory.
- Curves look faceted. Re-open with Fine. The geometry in the file is exact; only the display mesh changes.
After the STEP viewer: convert or compare
To print the part, use STEP to STL, which keeps the millimetre size you saw here. Going the other way, STL to STEP writes a faceted body. Each triangle becomes a flat face, about 1 KB per triangle, with no true cylinders. The older CAD exchange format has its own IGES file viewer. The application protocols and the rest of the background are in the STEP file guide, and every other format sits on the 3D model viewer hub.
Questions and answers
Is .stp the same as .step?
Yes. Both extensions name the same STEP format, and the picker on this page accepts both.
Do I need an account or an install to view STEP files online?
No. Open the page in Chrome or another Chromium browser and drop the file. Firefox and Safari have not been tested yet.
Can I edit the STEP part here?
Not as CAD features. You can measure, cut a section, check the bodies and convert to a mesh. Changing a hole diameter needs your CAD program.
Why does the first STEP take longer than the next one?
The tessellation engine is a 7.6 MB WebAssembly file that downloads once from our own domain. After that one download, later files skip the wait.
Does the STEP file reader show the weight of the part?
Yes, for a solid part in any of 17 materials, such as PLA at 1.24 g/cm³ or steel at 7.85 g/cm³. A % solid field covers printed infill.