Fillet Weld Leg Length Calculator
Calculate leg length, throat size, and minimum weld requirements.
AWS D1.1 Minimum Fillet Weld Size
| Base Metal Thickness | Min Fillet Size |
|---|---|
| ≤ 6mm (1/4") | 3mm (1/8") |
| 6-12mm (1/4" - 1/2") | 5mm (3/16") |
| 12-19mm (1/2" - 3/4") | 6mm (1/4") |
| 19-38mm (3/4" - 1-1/2") | 8mm (5/16") |
| 38-57mm (1-1/2" - 2-1/4") | 10mm (3/8") |
| 57-152mm (2-1/4" - 6") | 13mm (1/2") |
| > 152mm (6") | 16mm (5/8") |
Understanding Fillet Weld Dimensions
Key Formulas
- Theoretical Throat (equal leg): t = 0.707 x leg size
- Unequal Leg Throat: t = (a x b) / sqrt(a2 + b2) where a,b = leg sizes
- Weld Area: A = 0.5 x leg1 x leg2 (triangular approximation)
- Leg from Throat: leg = throat / 0.707 (for equal legs)
Effective vs. Theoretical Throat
The theoretical throat is the minimum distance from the root to the face. For processes with deep penetration (SAW, some GMAW), the effective throat may be larger than theoretical due to root penetration beyond the leg intersection.
Sizing Considerations
- Minimum Size: Based on thicker plate to prevent cracking during cooling
- Maximum Size: Should not exceed thinner plate minus 1.6mm (1/16")
- Strength Design: Size based on load requirements and allowable stress
- Overwelding: Avoid excessive size - wastes material and increases distortion