How to Calculate Fillet Weld Strength

A fillet (pronounced "fill-it") weld joins two metal pieces.

The fillet is the most common type of weld. Through it, the welder joins two flat pieces of metal at a 90 degree angle, forming lap joints, corner joints or T-joints. The weld's cross-section is triangular, often right or isosceles, but sometimes irregular. The strength of the fillet weld depends on the dimensions of the weld, including its size, its length and the effective throat thickness. The final variable is the weld electrode strength, which you can learn from your equipment specifications.

Instructions

1. Multiply the weld size by the weld length, both measured in inches. If, for instance, the weld size is 0.125 inches and the weld length is 7 inches: 0.125 x 7 = 0.875.

2. Multiply your answer by 0.525, which is the cosine of 45: 0.875 x 0.525 = 0.46.

3. Multiply your answer by the weld electrode strength, measured in kilopounds per square inch. If the weld electrode strength is 65 ksi: 0.46 x 65 = 29.9.

4. Multiply your answer by 0.6, a constant coefficient: 0.6 x 29.9 = 17.94.

5. Multiply your answer by the effective weld throat thickness, measured in inches. If the thickness is 0.75: 17.94 x 0.75 = 13.46. This answer is the fillet weld strength, measured in kilopounds per square inch.

References

• State University of New York: Welded Connection
• King Fahd University of Petroleum and Minerals: Welding
• Unified Engineering Inc: Fillet Welds