STEP Viewer
This is a simple viewer for 3D CAD models in STEP format (and also IGES and OpenCASCADE BREP files). Open a file from your computer to view it in 3D, rotate and zoom it, see the individual parts of an assembly and take measurements from it.
Your files stay on your computer. The viewer runs entirely in your web browser: the file is read and displayed on your own computer and is never uploaded to this (or any other) website.
Loading the STEP viewer…
How to use the viewer
| Action | Mouse | Keyboard |
|---|---|---|
| Rotate | Middle button drag (or left/right button drag) | Arrow keys (15°; with Shift: 90°) |
| Rotate about the axis out of the screen | Alt + middle button drag | Alt + Left/Right |
| Pan | Ctrl + middle button drag | Ctrl + arrow keys |
| Zoom | Scroll wheel (roll it away from you to zoom in; zooms towards the point under the mouse pointer), or Shift + middle button drag (up to zoom in) | Z / Shift + Z |
| Zoom to fit | Double-click the middle button | F |
| Select something to measure | Left click (Shift + click to select more than one) | Esc to clear the selection |
| Select or hide a whole part, or look straight at a face | Right click (or turn Measure off and click to select a part) |
To measure, make sure the Measure tool is on and click a face, edge or point: the measurements are shown at the bottom left. Shift + click a second item to measure between them (distances, angles etc.). Measurements are in millimetres (micrometres or metres for very small or large values); the buttons after each number copy it to the clipboard (in the unit shown, or in metres). Where a volume is shown (select a part, or an assembly, in the parts list), choose a material to see the mass: the first material chosen applies to every part; after that, choosing a material for other parts changes just those parts, so different parts can be different materials (select the top-level assembly to see the total mass). Hovering over a part in the parts list highlights it in the view.
The toolbar buttons (hover over them to see what they do) zoom to fit, orient the model with its Z or Y axis upwards (press again to turn it upside down), look directly at the XY, YZ or XZ plane or at a selected flat face (press again to look from the other side), lock rotation, switch between perspective and orthographic views (your choice is remembered; until you choose, the plane views switch to orthographic), change colours, show the list of parts in an assembly, and make the viewer fill the window or screen.
The cross-section button cuts through the model to show the inside. The cut can be parallel to the XY, YZ or XZ plane, or defined by what's selected: a flat face; a flat face and a point or edge (parallel or normal to the face, through the point or edge); or two flat faces (midway between them). The slider moves the cut and Flip shows the other side. You can select features inside the model while the cross-section is shown, then close it and Shift + click outside features to measure between them.
On a touch screen, drag with one finger to rotate, drag with two fingers to pan and pinch to zoom. Tap faces, edges or points to select them for measuring: each tap adds to the selection (tap something again to deselect it), and tapping the background clears it. Touch and hold for the menu (e.g. to select a whole part).
3D mouse
A 3Dconnexion SpaceMouse (or other 3Dconnexion 3D mouse) can be used to move the model around. This needs 3Dconnexion's 3DxWare 10 driver to be installed and running, so it only works on the operating systems that 3Dconnexion supports (Windows and macOS). When you enable it, the viewer connects to the driver on your computer, so your browser may ask for permission for this site to access apps and devices on your computer: allow it, and then reload the page if the 3D mouse doesn't work straight away. The setting is remembered for next time.
The STEP Viewer is free to use, for any purpose (including commercial use). It is provided “as is”, without warranty of any kind, and no liability is accepted for any loss or damage arising from its use, including from any inaccuracy in the display or measurements; always check critical dimensions against the original CAD data. © 2026 A. S. Budden. All rights reserved. It uses three.js (MIT licence) and Open CASCADE Technology (licensed under the GNU LGPL 2.1 with an exception), which reads the CAD files; the source code of Open CASCADE, and of the small interface that builds it into the viewer (so that you can rebuild that part with a modified Open CASCADE), is available on request. 3D input device development tools and related technology are provided under license from 3Dconnexion. © 3Dconnexion 1992 - 2025. All rights reserved.
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