Fillet weld strength calculator

Estimate fillet weld throat, capacity and the leg size needed for an applied load. Screening only, not a weld design.

Fillet leg size (mm)Weld length per side (mm)Number of welded sidesElectrode strength FEXX (MPa)Applied load to check (kN)

Throat thickness4.24 mm

ASD capacity122.2 kN

LRFD capacity: 183.3 kN. Utilisation of ASD capacity at 50 kN: 40.9%. Required leg for 50 kN (ASD basis): 2.46 mm. Check the AWS minimum leg size for the plate thickness as well; the minimum can govern over this calculation.

Safety-critical screening only: this is not a weld design or approval. A qualified person must verify the joint type, load direction, plate thickness, minimum leg size, electrode, WPS and inspection requirements under AWS D1.1 / AISC 360.

Formula

Throat = 0.707 x leg size. ASD capacity = 0.30 x FEXX x throat x length. LRFD capacity = 0.75 x 0.60 x FEXX x throat x length. Required leg (ASD basis) = applied load / (0.30 x FEXX x 0.707 x length).

Standard / source

AWS D1.1 and AISC 360 fillet-weld strength provisions, cited by reference only in the MetalCalz tool-expansion research (2026-10-27). No code table is reproduced here; check the AWS minimum leg size for the plate thickness separately, since the minimum can govern.

Worked example

Leg 6 mm, length 200 mm, one side, E70xx (FEXX 480 MPa): throat = 0.707 x 6 = 4.24 mm. ASD capacity = 0.30 x 480 x 4.242 x 200 = 122,170 N = 122.2 kN. LRFD capacity = 0.45 x 480 x 4.242 x 200 = 183.3 kN. Required leg for 50 kN (ASD basis) = 50,000 / (0.30 x 480 x 0.707 x 200) = 2.46 mm. These are the calculator defaults.

Safety note

Safety-critical screening only: qualified-person gate. This result is not a weld design, approval or compliance statement. A qualified person must verify joint type, load direction, plate thickness, minimum leg size, electrode, WPS and inspection requirements under AWS D1.1 / AISC 360 before welding a load-bearing joint.