Fillet Weld Volume Calculator
Compute the cross-section, volume and weld-metal weight of an equal-leg fillet weld from its leg size and length.
How it works
Cross-section = (leg² ÷ 2) × (1 + reinforcement) · Throat = 0.707 × leg · Volume = area × length · Weight = volume × 7.85 g/cm³
An equal-leg fillet weld is a right triangle whose two legs meet at the joint, so its ideal cross-section is leg² ÷ 2. The effective throat — the shortest distance from the joint root to the face, and the dimension that carries load — is 0.707 times the leg. Real welds carry a convex crown of extra metal above the flat face, so a reinforcement allowance of about 10% gives a more honest volume for estimating filler and cost.
Worked example
An 8 mm fillet, 1000 mm long, with 10% reinforcement: cross-section = (8² ÷ 2) × 1.10 = 35.2 mm²; volume = 35.2 × 1000 = 35,200 mm³ = 35.2 cm³; weight = 35.2 × 7.85 ÷ 1000 = 0.276 kg. The effective throat is 0.707 × 8 = 5.66 mm.
Frequently asked questions
What is the throat of a fillet weld?
The effective throat is the shortest path from the weld root to the face — for an equal-leg fillet it equals 0.707 × leg. It is the dimension used in strength calculations, so a larger leg buys proportionally more throat.
Why add a reinforcement percentage?
A finished fillet is usually slightly convex, carrying more metal than the flat theoretical triangle. Adding roughly 10% reflects that crown so your filler-metal and cost estimates are not short.
Does this work for unequal-leg fillets?
This assumes equal legs. For an unequal fillet, the cross-section is (leg1 × leg2) ÷ 2; enter an equivalent equal leg or scale the result if your two legs differ significantly.
Related calculators
This calculator is for educational purposes. Double-check important results before acting on them.