Check a fillet weld leg size against shear, axial and bending load. Returns effective throat, weld area, combined stress, allowable stress and utilisation, plus the AWS D1.1 minimum leg size for the joint.
A fillet weld is checked on its effective throat — the shortest distance from the weld root to the face. For a 45° equal-leg fillet that is 0.707 times the leg size. All stress is referred to that throat area, never to the leg.
w leg size (mm) ·
a effective throat (mm) ·
Lw weld length (mm) ·
n number of weld lines ·
V shear (kN) ·
N axial (kN) ·
M moment (kN·m) ·
FEXX electrode tensile strength (MPa)
A bracket is attached with an 8 mm double-sided fillet weld, 250 mm long each side, carrying 120 kN of direct shear. Electrode is E70XX.
The weld is lightly loaded at under 30 % utilisation. Reducing to a 6 mm leg would raise utilisation to about 39 %, still comfortable, and would cut weld metal volume by roughly 44 % since deposit volume scales with the square of the leg.
| Quantity | Symbol | Unit | Accepted range |
|---|---|---|---|
| Leg size | w | mm or in | > 0 |
| Weld length | Lw | mm or in | > 0 |
| Shear force | V | kN, N or kip | ≥ 0 |
| Axial force | N | kN | ≥ 0 |
| Bending moment | M | kN·m | ≥ 0 |
| Electrode strength | FEXX | MPa | > 0 |
| Effective throat | a | mm | output |
| Throat area | Aw | mm² | output |
| Combined stress | τtot | MPa | output |
Imperial inputs are converted before calculation: 1 in = 25.4 mm and 1 kip = 4.44822 kN. All internal work is done in SI.
| Classification | FEXX (MPa) | Allowable 0.30·FEXX (MPa) |
|---|---|---|
| E70XX | 480 | 144 |
| E80XX | 550 | 165 |
| E90XX | 620 | 186 |
| Thicker part joined | Minimum leg (mm) |
|---|---|
| Up to 6 mm | 3 |
| Over 6 to 12 mm | 5 |
| Over 12 to 19 mm | 6 |
| Over 19 mm | 8 |
For a standard 45° equal-leg fillet the effective throat is 0.707 × leg size, because the throat is the perpendicular distance from the root to the hypotenuse of a right isosceles triangle. An 8 mm leg gives a 5.66 mm throat. For a complete joint penetration butt weld the throat equals the plate thickness. For a partial penetration weld this calculator uses the greater of leg − 3 mm or 70 % of the leg.
This calculator uses 0.30 × electrode tensile strength, the AWS D1.1 and AISC allowable shear stress on the effective throat area. For an E70 electrode at 480 MPa the allowable is 144 MPa. For E80 at 550 MPa it is 165 MPa, and for E90 at 620 MPa it is 186 MPa.
AWS D1.1 sets a minimum leg size based on the thickness of the thicker part joined, to ensure the weld cools slowly enough to avoid cracking. This calculator applies 3 mm up to 6 mm material, 5 mm up to 12 mm, 6 mm up to 19 mm and 8 mm above that. The minimum is a fabrication requirement and applies even when the strength calculation permits a smaller weld.
Direct shear produces a stress of V / Aw. Axial force and bending produce a normal stress on the throat. The two are combined using a von Mises style relationship in which the normal component is divided by √3 before being added in quadrature to the shear component. The result is compared against the allowable shear stress on the throat.
A double-sided fillet doubles the effective weld area for the same leg size and length, halving the stress. It also balances the joint and reduces angular distortion from one-sided shrinkage. Single-sided welds are used where access is restricted, but they induce eccentricity and should not be used for joints carrying significant bending about the weld line.