Weld seam calculator

The formula

For an equal-leg fillet weld (90°, both legs the same length) with throat thickness a, the theoretical cross-section is a right triangle with area a².

theoretical cross-section = a²
actual cross-section = a² × (1 + convexity allowance)
weight (kg) = cross-section (m²) × seam length (m) × density (kg/m³)

A real weld bead is never perfectly flat — convexity typically adds 10-30% more material than the theoretical triangle. This tool defaults to 20%, adjustable to whatever is typical for your process.

This calculator applies to fillet welds. Butt welds (with V, X or U preparation) depend too much on the exact preparation and gap for a generic formula — send the drawing and we'll verify it.

Material densities

Filler metal has a slightly different density than the base material, but for a first estimate that difference is negligible.

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