Welding Calculator
Estimate the strength of weld joints using the welding calculator.
Weld capacity44,541 lb22.271 US tons · 198.1 kN
Effective throat0.17675 in0.707 × the leg size
Effective area2.121 in²2 welds of 6 in
Allowable shear stress21,000 psi0.3 × 70,000 psi electrode
Capacity per inch of weld3,711.8 lb/in
Weld metal volume0.375 in³a triangular section
Minimum leg for this thickness0.125 inAISC minimum fillet size, to avoid cracking from rapid cooling
Maximum leg on a plate edge0.25 ina fillet on the edge of plate over ¼ in must be 1/16 in less than the plate
The formula
fillet weld capacity = 0.707 × leg × length × allowable shear
The throat is 0.707 of the leg
A fillet weld has a triangular section, and it fails across its shortest dimension — the throat, running from the root to the face. For an equal-leg fillet that is the leg divided by √2, or 0.707 of it. Doubling the leg size doubles the strength but quadruples the weld metal and the heat, which is why two smaller welds usually beat one large one.
These are allowable-stress figures for statically loaded joints. Fatigue is a different problem entirely, and it is governed by the geometry at the weld toe far more than by the size of the weld.