STL 3D Model Inspector (Volume, Bed Fit)

How to use

1. Drop a .stl file onto the dashed area or use the Choose file button.
2. Switch units between mm, cm, m, and inches (STL files don't store units, so mm is the universal print convention).
3. Inspect the stat grid, three orthographic projections, and the bed-fit table to see which printers will accept the part.
4. Click Reset to load a different file.

Frequently asked questions

Is my STL uploaded?

No. The file is read with file.arrayBuffer(), parsed and rendered entirely in your browser — nothing goes to a server. You can verify by watching DevTools → Network when you load a file.

What does 'watertight' actually mean here?

Every interior edge in a closed mesh is shared by exactly two triangles. This tool builds a map of undirected edges and checks the count: anything but 2 means a hole, an unwelded duplicate vertex, or a non-manifold join. Slicers like PrusaSlicer / OrcaSlicer can sometimes repair small holes automatically, but a watertight mesh is required for a reliable solid volume calculation.

How is volume computed?

By the signed-tetrahedron method: every triangle (v₀, v₁, v₂) and the origin form a tetrahedron with signed volume (v₀ · (v₁ × v₂)) / 6. Summing across all triangles gives the enclosed volume — exact for any closed surface, regardless of where the origin is. The shown value is the absolute value so winding-order issues don't flip the sign.

STL has no unit info — what unit is the file in?

STL doesn't encode units. The de-facto convention for 3D printing is millimeters; for CAD exchange it's often inches. If a 100 mm cube measures 100 in this tool, it's mm. If it measures 3.94, it's probably inches. Switch units in the dropdown until the numbers match expectation.

Why is the preview just line outlines, not shaded?

Because SVG without WebGL can comfortably handle thousands of line segments but not depth-sorted filled polygons with shading. The orthographic outline view still tells you the silhouette and gives a quick sanity check on orientation and size — for full 3D rendering, open the STL in a slicer or a viewer like Cura / Bambu Studio.

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