Welding Calculator
Find the required fillet weld leg size for a given load, or the load capacity of a fillet weld you already have sized.
Enter your values
Choose direction, then fill in the fields below.
How this calculator works
For an equal-leg fillet weld loaded in shear along its length, the effective throat thickness is 0.707 times the leg size — the shortest distance from the weld root to the theoretical hypotenuse face. Load capacity is:
L is total weld length and τ_allow is the allowable shear stress of the weld metal. Rearranged for required leg size given a known load:
Typical allowable weld shear stress
| Electrode / weld metal | Typical allowable τ |
|---|---|
| E60XX | 96 MPa |
| E70XX | 110 MPa |
| E80XX | 128 MPa |
These are general reference figures based on common allowable-stress design practice — always confirm against the applicable welding code and electrode datasheet.
Frequently asked questions
Does this apply to groove (butt) welds too?
No — groove welds are typically sized to match the base metal thickness and checked against the base metal's allowable stress directly, without the 0.707 throat factor used for fillets.
Should I include both sides of a double fillet weld?
Yes — if the joint is welded on both sides, add the length of both welds together as your total weld length, L, before calculating.