Cross Section Viewer

How to view the cross-section of an STL file

A cross-section is the outline you get when you cut a 3D model with a flat plane — the same shape you would see if you sawed the part in half and looked at the cut face. iamRapid's free online cross-section viewer reads your STL or OBJ entirely in your browser, intersects every triangle of the mesh with a cutting plane, and draws the exact section outline. It is the quickest way to see the inside of a 3D model without any CAD software.

For each slice the tool computes the section in two ways at once: a 2D cross-section trace — the real line segments where the plane cuts the surface, auto-scaled in millimetres — and a 3D clipped view, where a clipping plane hides everything on one side so you can rotate the part and look straight into the cut.

What a cross-section (slice) shows you

• Hidden internal geometry — cavities, channels, ribs and pockets that are invisible from the outside.
• Wall thickness — how thick the shell is at the cut, so you can confirm a hollowed part has enough material to print. For a dedicated check, use the wall thickness analysis tool.
• Enclosed voids and trapped volume — closed inner contours reveal sealed pockets that can trap powder or uncured resin and need a drain or escape hole.
• Shell continuity — whether the part is a single solid wall or breaks into separate fragments at that plane.
• Section dimensions in mm — the width and height of the slice, read straight off the 2D trace.

Every outline is computed from your actual mesh by triangle–plane intersection — nothing is estimated or faked. Before slicing, the file is welded with the same mesh engine used by our STL analysis and STL repair tools, so coincident vertices are merged and the contours close cleanly.

How to slice a 3D model online (step by step)

1. Upload your file using the dropzone above — drag in an STL or OBJ, or click to browse. The file is read locally in your browser and never uploaded to a server.
2. Choose a slice axis — pick X, Y or Z to set the direction the cutting plane faces.
3. Move the position slider — drag across the bounding box to move the plane through the part. The current slice position is shown in millimetres.
4. Read the cross-section — the 2D trace draws the section outline auto-scaled to fit, while the 3D clipped view lets you rotate the cut model.
5. Take the next step — if the section reveals trapped voids or thin walls, fix the model or add drain holes, then get an instant 3D printing quote when it's ready.

No signup or software installation required. The viewer works directly in your browser on any device.

Why check cross-sections before 3D printing?

Looking at a model from the outside tells you nothing about its interior. A cross-section exposes the geometry a slicer will actually print: wall thickness that may be too thin to survive, enclosed cavities that trap powder or resin, and internal features that should connect but don't. Catching these in the section view — rather than after a failed print — saves material, time and cost. Once your part checks out, get an instant quote from iamRapid for online FDM, SLA, SLS, MJF and PolyJet 3D printing across India, or explore the full suite of free 3D printing tools.