How to see inside a 3D model with Section
Cut a 3D model along X, Y or Z in STL Viewer, slide the plane through it and read the section's width, height and area to check walls and cavities.
Section cuts the model with a flat plane so you can look inside: check wall thickness, hidden channels, how a hollow part is built or whether a cavity is closed. The cut face is drawn solid, and the app gives you the size and area of the section. Section is a Premium tool.
Cut a section
- Open the model and tap Section in the tools.
- Under Cut across axis, choose X, Y or Z. In most 3D print files Z is the height, so a Z cut is horizontal, like a layer on the print bed, and X and Y cut vertically.
- Move the Section position slider to slide the plane through the model. The cut updates as you move it.
- Tap Show other side to see the opposite half.
- Rotate and zoom as usual to look at the cut face from any angle. Close the tool to see the whole model again.
What the numbers mean
- Section shows the width and height of the cut face, the size of the outline at that position.
- Area is the area of the solid cut face. On a Z cut it is the area of that layer, which tells you how much the printer has to fill at that height.
Turn on Axes in the toolbar first so you know which way X, Y and Z point on this model (see view modes).
Messages you may see
| Message | What it means |
|---|---|
| Open outline: the model isn't watertight here. | The mesh has a hole at this height, so the cut can't be closed. Check the watertight result in Model info. |
| The plane doesn't cut the model here. | The slider is beyond the model. Move it back. |
| Approximate: cut through the simplified view. | The model is very large and shown simplified, so the outline is close but not exact. |
| There isn't enough free memory to show this cut. | Close other apps and try again, or use a smaller file. |
Section or x-ray?
X-ray mode (free) makes the surface see-through so you can get a quick idea of the inside. Section shows a real, solid cut with numbers, which is better for checking a wall thickness or a hole that must stay open.
Premium
Section is part of Premium, a one-time purchase or a yearly subscription. Premium also unlocks Measure, Scale & export and Compare and removes ads.
More examples in our article on cross-sections of STL files.
Learn more on the blog
- STL Cross Section: Check Wall Thickness and Hidden Gaps Inside
- Watertight Mesh: What It Means and Why 3D Prints Fail Without It
Questions and answers
What does 'Open outline' mean?
The mesh has a hole or open edge where the plane cuts it, so the section can't be closed. The model isn't watertight at that point.
Which axis cuts like a print layer?
In most 3D print files, the Z axis. A Z cut is horizontal, like one layer on the print bed, and its area shows how much the printer fills at that height.
Is Section free?
No, Section is a Premium tool. The free x-ray view mode lets you look through the surface without cutting.
More guides
- How to open STL, OBJ, 3MF and PLY files on Android
- How to use view modes and gestures in STL Viewer
- How to check a 3D model's size and volume
- How to estimate filament for a 3D print
- How to measure a 3D model in STL Viewer
- How to scale a 3D model and export it as STL
- How to compare two 3D models side by side
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