Work out weld size instantly with clear inputs, formula shown and shareable results.
A fillet weld carries load across its throat, which for an equal-leg weld is 0.707 times the leg size. Required throat is load divided by allowable stress times effective length, and the leg follows. Codes also impose a minimum leg for the plate thickness so the weld cools slowly enough to avoid cracking.
Throat required
Throat = load / (allowable stress x effective length)
Leg size
Leg = throat / 0.707, subject to the code minimum for plate thickness
Preliminary estimate only. Weld design and procedure must be verified by a qualified welding engineer against the governing structural welding code.
Throat = load / (allowable stress x effective length). A fillet weld carries load across its throat, which for an equal-leg weld is 0.707 times the leg size.
A small weld on thick plate cools very fast, hardening the heat affected zone and risking cracking. The minimum leg ensures adequate heat input for the section.
This calculator takes 4 inputs: Thinner plate thickness, Design load on weld, Effective weld length, Allowable weld stress. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.