3D Mesh Analyzer (STL, OBJ, PLY)

What it is for

3D Mesh Analyzer reads a triangle mesh and tells you whether it is a closed solid and what it measures. Upload a binary or ASCII STL, an OBJ, or an ASCII or binary PLY, or paste a small ASCII file. You get volume, surface area, the axis-aligned bounding box, a box aligned with the part's main directions, the centroid, holes, edges shared by too many triangles, flipped triangles, separate parts and a material estimate.

Use it before sending a part to a slicer or print service, when an exported model "looks fine" but a slicer complains, or when you need a weight and filament figure for a quote. It does not repair anything; the companion 3D Mesh Repair tool does that. It also does not detect self-intersections or thin walls.

Worked example

The first example is a 20 mm calibration cube as ASCII STL, with PLA selected. The summary reads "Watertight mesh: 8 cm³ volume, 24 cm² surface, 12 triangles." The topology table shows 8 vertices, 18 edges, no open boundary edges, an Euler characteristic of 2 and genus 0, exactly what a closed box should have. PLA at 1.24 g/cm³ gives a solid mass of 9.92 g and 3.326 m of 1.75 mm filament.

The second example is a 30 mm sphere as binary STL in PETG with 15 % infill and a 1.2 mm shell. Its 1,280 triangles enclose 14.0155 cm³, a little under the 14.137 cm³ of a perfect sphere because flat facets cut the curve. The shell estimate is 3.37675 cm³, the printed volume 4.97257 cm³ and the printed mass about 6.315 g, compared with 17.8 g solid.

The third example pastes an OBJ box whose top is missing and whose bottom has one flipped triangle. The callout reports one open hole with 4 boundary edges and 3 edges joining triangles with opposite winding, and warns that volume and material figures are not reliable. The shown 5.33333 cm³ is indeed meaningless for an open shell.

How to read the result

Watertight is the headline. It requires every edge to be shared by exactly two triangles that run along it in opposite directions, and no vertex where separate surface fans touch. Only then is the divergence-theorem volume a true enclosed volume. Inside out means the mesh is closed but its normals point inward; the volume shows as negative.

Holes counts groups of open edges, separate parts counts pieces connected through shared edges. The PCA box follows the part's main directions, so a rotated slab shows its real length, width and thickness. It is not guaranteed to be the smallest possible box. Triangle quality is 1 for an equilateral triangle; values below 0.1 are listed as slivers.

Tips and common mistakes

• STL and PLY store no units. A part drawn in inches and read as millimetres is 25.4 times too small in each direction; pick the right Model units.
• Keep Vertex welding on Automatic for STL files from CAD. Use Loose only for exports with visible cracks between facets.
• The infill figure treats surface area × shell thickness as solid and fills the rest at your percentage. Slicers add top and bottom layers differently, so expect differences.
• A resin preset gives mass but no filament length.
• Several separate parts are counted together; overlapping parts count their shared volume twice.

FAQ

Why is my volume negative?

The mesh is closed but inside out. Run it through 3D Mesh Repair to turn the normals outward.

Is my file uploaded?

The form sends the file to the usefulweb server for this one calculation. Renderloom Mesh Lab runs the same engine entirely in your browser, without any upload.

What are the size limits?

30 MB per file and 500,000 triangles.

Why does a closed mesh still show non-manifold vertices?

Two parts touch at a single corner. Many slicers accept this, but some print services reject it.