STL analyzer: check volume, size, holes and weight before the slicer
Choose an STL file and read its volume, area, size in mm, estimated weight and material cost, and whether the surface is closed. Everything is calculated in your browser, and the file never goes to a server.
Opens without an account 3 times a day. A free account removes the limit.
- Volume in cm³from the surface of the model
- Holes in the modela count of boundary edges
- 9 materialswith a price and a density
- 220 × 220 × 250 mmindicative printer size it checks
What an STL file check shows
The STL analyzer is a free online tool from EduFacturing that reads an STL file and shows the triangle count, volume, surface area, size and whether the surface is closed. It adds an estimated weight and material cost for nine materials, and printability warnings based on FDM rules.
An STL describes only the outer shell with triangles, with no interior and no units, so the volume is worked out from the shell and the coordinates are read as millimeters.
Volume, size, weight and holes of an STL file
Shows the STL file in 3D
It reads binary and ASCII STL and builds the model in a 3D view you rotate with the mouse. One button colors it by height.
Volume, size and holes
It shows the triangles (and the degenerate ones, if any), volume in cm³, area in cm², size along X, Y and Z in mm, and the boundary edge count, which points to holes.
Weight and cost of the material
Choose one of 9 materials (PLA, ABS, PETG, TPU, ASA, Nylon PA12, PC and two resins) and an infill from 0 to 100% in steps of 5. You get the weight in g and the cost in EUR.
Printability warnings
It checks the size against 220 × 220 × 250 mm, the thinnest axis against 0.8 mm, and the size ratio against the limits 3 and 8. Every warning links to the 3D printing design rules.
When to check an STL file before you print
A model often comes from someone else, and nobody says whether it is fit to print.
Checking someone else's file
You get an STL from a colleague or a client. Before the slicer, you see whether it is watertight and whether the size makes sense.
How much the material weighs and costs
A rough weight and material cost at a chosen material and infill, before you name a price. Machine time and labor are not included.
A 3D printing lesson
A teacher shows how volume comes from triangles and why 50% infill is not half the weight.
How STL volume is calculated and holes are found
A change of material or infill recalculates only the weight and cost. The geometry is calculated once, when the file loads.
Volume, area and size
An STL has no units, so coordinates are read as millimeters. The volume sums one tetrahedron per triangle, with its apex at the origin; the area sums the triangle areas, and the size comes from the extreme coordinates on each axis.
Holes (watertightness)
Every edge is recorded by the coordinates of its vertices, rounded to 0.0001 mm, and the triangles on it are counted. In a closed surface there are exactly two. An edge on one triangle is a boundary edge and means a hole, and an edge on more than two also makes the model not watertight.
Weight and printability
The weight is volume times density times the infill share plus 0.15 for the walls, capped at 1. The printability check compares the size with three rules: printer size, minimum wall and size ratio.
| Applies to | Formula | Meaning |
|---|---|---|
| Volume | V = |Σ v₀·(v₁ × v₂)| / 6 | sum over the triangles, in mm³; shown in cm³ |
| Area | A = Σ ½·|(v₁ − v₀) × (v₂ − v₀)| | sum of the triangle areas, in mm²; shown in cm² |
| Weight and cost | m = V·ρ·min(1, i + 0.15) and C = m / 1000 · price per kg | V in cm³, ρ in g/cm³, i is the infill from 0 to 1; m is in g, C is in EUR |
| Size ratio | k = longest side / shortest side | ignoring zero sides; 3 and up is a warning, 8 and up is an error |
What is different: holes as a number, no upload
Holes are a number
Watertightness is a count of boundary edges, not an impression: above 0, they are the edges around the holes.
Thresholds come from the EduFacturing rules
The 0.8 mm wall and the limits 3 and 8 come from the FDM rules, not typed in by hand. The 220 × 220 × 250 mm size is separate and indicative.
The tool does not slice the model and gives no print time, supports or exact weight. Weight and cost cover the material only, from an approximate formula, with no electricity, machine wear or labor. It does not repair holes or export a file. On a model that is not watertight, the volume and weight cannot be trusted.
The printability check looks only at the size of the whole model, with FDM rules even when a resin is chosen. A thin wall inside, overhangs and bridges are not seen. The 220 × 220 × 250 mm size is fixed, and sides are sorted by length before comparing, so a model passes if it fits with its axes in any order.
Questions about checking an STL file
How to check if STL is printable and free of holes?
Upload it and read the boundary edge count: a closed surface (a watertight model) has none, and a number above 0 means the edges around holes. Printability warnings (size, thinnest axis, ratio) appear separately. Holes are not repaired.
How to see the dimensions of an STL file?
Upload the file and the size along X, Y and Z shows in mm. An STL has no units, so the coordinates are read as millimeters.
How to calculate volume of a 3D model from an STL file?
The volume sums one tetrahedron per triangle: V = |Σ v₀·(v₁ × v₂)| / 6. For a closed surface the sum is the exact volume, shown in cm³.
How much filament do I need for a model?
The tool gives the weight of the material in g for the chosen material and infill, not the filament length. Example: PLA, 32.14 cm³ and 20% infill give 13.9 g and 0.31 EUR.
Why does 50% infill not give half the weight?
The tool adds 0.15 for the walls: at 50% it counts 65% of the solid weight, and at 20% it counts 35%.
Can I use it as an STL viewer online?
Yes, for looking: the model shows in a 3D view you rotate with the mouse and color by height.
Is the STL analyzer free?
Yes. Without an account it opens 3 times a day, and a free account removes the limit.
The STL analyzer is free. Pro opens the rest
Pro costs 15 EUR a month and opens 45 Pro tools.
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