Which term describes the distance used to estimate design strength for fillet welds?

• A. Theoretical Throat
• B. Effective Throat
• C. Leg Length
• D. Weld Length

Answer: (A)

For fillet welds, the strength is governed by the throat thickness—the perpendicular distance through which the weld material actually resists shear. This distance, called the theoretical throat, is the ideal cross-section used to estimate design strength. The leg length tells you how long the weld runs along each member, and weld length is just the length of the weld along the joint; neither directly defines the load-carrying cross-section. The theoretical throat represents the minimum cross-sectional area that carries the load, so it’s the measure used in design calculations. For a 45-degree fillet, the theoretical throat is the leg length divided by the square root of two. If reinforcement changes the effective cross-section, the concept of an effective throat comes into play, but for basic design estimates the theoretical throat is the key distance.