3.18.2 Size of Fillet Welds – Equal Leg Fillet Welds
The strength of a fillet weld is governed by both the fillet size and the effective throat thickness. The
fillet size is the length of the side of the largest triangle that can be inscribed within the weld crosssection
as shown in Figures 3.50 and 3.51. For equal leg convex fillet welds, the measured leg size is
the fillet size as shown in Figure 3.50. For equal leg concave fillet welds, the fillet size is the side of
the inscribed triangle, or the theoretical effective throat multiplied by 1.4 as shown in Figure 3.51.
1) The Specified Size is the size as it appears in the welding symbol and is designated by
the letter “S”.
2) The Effective Size is the size that corresponds to the specified size and is designated by
the expression “S effective” = “Seff”.
3) The Measured Size is the size established on the basis of measurement and is
designated by the term “S measured” = “Sm”.
These sizes for the following three types of fillet welds are as shown in Figure 3.59.