Fillet Weld Capacity Calculator
Plan your materials specifications project with our free fillet weld capacity calculator. Get precise measurements, material lists, and budgets.
Reviewed by Abdullah, Technical Content Specialist
Formula
Design Strength = phi x 0.6 x FEXX x Throat x Length
The design shear strength of a fillet weld equals the resistance factor (phi = 0.75 for LRFD) multiplied by 0.6 times the electrode tensile strength, times the effective throat thickness (leg x 0.707), times the weld length. The 0.6 factor converts tensile strength to shear strength.
Worked Examples
Example 1: E70 Fillet Weld on Steel Beam
Problem:Calculate the design capacity of a 6mm fillet weld, 200mm long, using E70 (490 MPa) electrodes with LRFD phi = 0.75.
Solution:Throat = 6 x 0.707 = 4.243 mm\nEffective Area = 4.243 x 200 = 848.53 mm2\nNominal Strength = 0.6 x 490 x 848.53 = 249,468 N = 249.47 kN\nDesign Strength = 0.75 x 249.47 = 187.10 kN
Result:187.10 kN design shear capacity
Example 2: E60 Weld for Light Structure
Problem:Find the capacity of a 5mm fillet weld, 150mm long, using E60 (414 MPa) electrodes.
Solution:Throat = 5 x 0.707 = 3.536 mm\nEffective Area = 3.536 x 150 = 530.33 mm2\nNominal = 0.6 x 414 x 530.33 = 131,734 N\nDesign = 0.75 x 131.73 = 98.80 kN
Result:98.80 kN design shear capacity
Frequently Asked Questions
What is the throat thickness of a fillet weld?
The effective throat thickness of a fillet weld is the shortest distance from the root of the joint to the face of the weld. For equal-leg fillet welds, this equals the leg size multiplied by the cosine of 45 degrees, which is the leg size divided by the square root of 2 (approximately 0.707 times the leg size). This throat dimension is critical because it represents the weakest cross-section of the weld where failure would occur under shear loading.
How is fillet weld capacity calculated per AISC standards?
Per AISC 360, the design shear strength of a fillet weld is calculated as phi times 0.6 times the electrode tensile strength (FEXX) times the effective throat area. The resistance factor phi is 0.75 for LRFD design. The effective area equals the throat thickness multiplied by the weld length. For E70 electrodes (70 ksi or 490 MPa), the allowable shear stress on the weld metal is 0.6 times 490 equals 294 MPa nominal.
What is the minimum and maximum fillet weld size?
The minimum fillet weld size depends on the thicker plate being joined, per AISC Table J2.4. For plates up to 6mm (1/4 inch), minimum leg size is 3mm (1/8 inch). For plates 6-13mm, minimum is 5mm (3/16 inch). The maximum fillet weld size along an edge should not exceed the plate thickness minus 1.6mm (1/16 inch) for plates thicker than 6mm. These limits ensure proper fusion and prevent burn-through on thin members.
How do I calculate the load-bearing capacity of a beam?
Beam capacity depends on material, cross-section dimensions, span length, and support conditions. For a simple rectangular wood beam, bending strength = (F_b x b x d^2) / 6, where F_b is allowable stress, b is width, and d is depth. Always consult a structural engineer for critical applications.
References
Reviewed by Abdullah, Technical Content Specialist · Editorial policy