How to check a 3D model's size and volume
Use Model info in STL Viewer to see width, depth and height, volume, surface area, triangles and whether the mesh is watertight, in mm or inches.
Model info answers the questions you have before printing: how big is this part, will it fit my printer, and is the mesh closed so a slicer can handle it? It is free and works offline.
Open Model info
- Open a model (see how to open files).
- Tap the Model info button (i) in the top bar. On a tablet, the info appears in the side panel.
- Scroll the panel to see the size, the mesh details and the filament estimate.
What each value means
| Value | Meaning |
|---|---|
| Size (W × D × H) | Width, depth and height of the model's bounding box, in mm or inches. Compare it with your print bed. |
| Volume | The space the solid model takes up, in cm³ or in³. It is the base for the filament estimate. |
| Surface area | The total area of the outer skin, in cm² or in². |
| Triangles | How many triangles the mesh has. More triangles mean finer detail and a bigger file. |
| File size, Format | The size on disk and the format, such as STL (binary) or STL (ASCII). |
| Parts | For 3MF files with several objects. |
| Watertight | Whether the mesh is closed, with no holes or open edges. |
The watertight check
A printable model should be a closed shell. The check gives one of these answers:
- Yes: the mesh is closed, so volume and filament are reliable.
- No, it has holes or open edges: the volume can't be measured reliably. Repair the model in your 3D software or let your slicer try to fix it.
- Yes, but some faces point inward: the shell is closed, but some normals are flipped, which also makes the volume unreliable.
- Not checked: the check was skipped, and the volume assumes the model has no holes.
Millimeters or inches
STL, OBJ and PLY files store no unit, so STL Viewer assumes millimeters. If a model looks about 25 times too small, it was probably drawn in inches: open File units for that model and choose inches. The app remembers this for the file. 3MF files declare their own unit, shown as "Set by the file".
Which unit the numbers are shown in is a separate choice: change Units in Settings to millimeters or inches.
For very large models the screen may show a simplified view, but every number in Model info is calculated from the full mesh.
Need the distance between two specific points rather than the overall size? Use Measure. To learn why closed meshes matter, read what a watertight mesh is.
Learn more on the blog
- Watertight Mesh: What It Means and Why 3D Prints Fail Without It
- STL Inches to mm: Fix a Model That Prints Too Small or Too Big
- Check Your STL Before Printing: An 8-Point Checklist
Questions and answers
Why is my model tiny?
It was probably drawn in inches, while STL files store no unit and millimeters are assumed. Switch the File units of that model to inches.
What does 'No, it has holes or open edges' mean?
The mesh isn't closed, so its volume and the filament estimate can't be measured reliably. Repair it in your 3D software or slicer before printing.
Is the size the size of the printed part?
It is the bounding box of the mesh: the width, depth and height of the smallest box around the model, in the unit you chose.
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 estimate filament for a 3D print
- How to measure a 3D model in STL Viewer
- How to see inside a 3D model with Section
- How to scale a 3D model and export it as STL
- How to compare two 3D models side by side
Check your next print on your phone
Free STL, OBJ, 3MF and PLY viewer for Android. Works offline.