Fillet Weld Calculator
Weld inputs
Fields start empty. Enter your own values, or load the worked example to see how it works.
Enter decimals, e.g. 0.25 for 1/4 in.
Nominal, approximate densities. Individual alloys in each family vary; use a custom density for your filler metal if it matters.
Enter your values (or load an example) to see results. Fix any highlighted inputs.
What this calculates
An ideal equal-leg fillet is a right triangle with both legs equal to the leg size z. This calculator finds the triangle's area, multiplies by length for volume, then by density for weight. It is pure geometry.
Real welds carry extra metal: convexity (reinforcement), unequal legs and penetration into the base metal all change the deposited amount. A convex weld can hold noticeably more metal than the ideal triangle. Treat the result as a baseline.
Formula
A = z² ÷ 2 (cross-section area) V = A × L (volume, L converted to in or mm) W = V × density (weight / mass)
Units: inches → in², in³, lb (density in lb/in³). Millimeters → mm², then cm³ (÷ 1,000) and kg (g/cm³ × cm³ ÷ 1,000).
Worked examples
1/4 in fillet, 10 ft, carbon steel (nominal 0.2836 lb/in³) A = 0.25² ÷ 2 = 0.03125 in² V = 0.03125 × 120 in = 3.75 in³ W = 3.75 × 0.2836 = 1.06 lb 6 mm fillet, 1 m, carbon steel (nominal 7.85 g/cm³) A = 6² ÷ 2 = 18 mm² V = 18 × 1,000 mm = 18,000 mm³ = 18 cm³ W = 18 × 7.85 = 141 g = 0.141 kg