Fillet weld size

Use effective weld length

Count only the length that participates in the load path under the chosen design method. Check whether the drawing specifies leg size or throat size; they are not interchangeable. The entered stress allowance must suit the weld material, process, and applicable design basis.

Direct shear is a limited load case

An eccentric force can create a moment that changes the stress distribution along the weld. This simple calculation does not check that condition, fatigue, base-metal failure, or weld quality. Use a suitable weld-group analysis and the relevant design requirements where those effects matter.

Using throat area rather than visible leg area

For an ideal equal-leg fillet, a 6 mm leg corresponds to a throat of about 4.24 mm. Multiplying by 100 mm of effective weld length gives about 424 mm² of throat area. The direct-shear stress is applied force divided by that area. Using leg size directly as throat would overstate the resisting area in this geometry.

When the same force is shared by several parallel weld lengths under the model's assumptions, use their combined effective length. Do not count unwelded gaps or inaccessible portions of a nominal joint line. If the load is offset from the weld group's center, a moment changes the distribution and a direct-force division alone is insufficient. Check whether the specified allowable is compatible with the design method and weld geometry. The calculation does not assess penetration, defects, fatigue category, or the strength of the attached base material. Record the required effective size and length clearly, then verify that the drawing and welding procedure actually provide them.

Formula

Effective throat = leg/√2; direct resistance = throat × effective length × allowable.