Fillet Weld Strength Calculator
Load capacity of a fillet weld from the electrode classification, the leg size and the weld length, using the 0.6 FEXX shear strength on the effective throat with the transverse load angle factor. Results include the throat thickness, the shear stress on the throat, the utilisation against the applied load, and the leg size needed to carry that load at a chosen safety factor.
How to use this calculator
- Enter the weld leg size written on the drawing, and the effective length of the weld run measured along its axis.
- Enter the angle between the load and the weld axis, where 0 degrees is a longitudinal weld in pure shear and 90 degrees pulls across the weld.
- Enter the electrode classification strength, which is 490 MPa for E70XX and 415 MPa for E60XX, and the applied service load.
- Read the throat thickness, the nominal and allowable strengths, the shear stress on the throat, and the leg size that would be needed for the applied load.
Frequently asked questions
Why is the throat thickness 0.707 times the leg size?
A fillet weld of equal legs has a triangular cross section, and the throat is the shortest distance from the root to the hypotenuse, which is the leg size times the sine of 45 degrees. Failures are observed to run along that plane, so it is the plane the strength calculation uses. An unequal legged weld changes the geometry and the smallest throat governs.
Why is a transverse weld stronger than a longitudinal one of the same size?
A load across the weld axis has to rotate the failure plane before it can slide along it, and the constraint around the root makes that harder, so tests show an increase of up to 50 percent over a load along the axis. The angle factor in the code reflects this. Using a factor of 1.0 for every weld is conservative, is permitted, and is often the simplest thing to do.
What is the minimum fillet weld size I am allowed?
It scales with the thickness of the thicker part being joined, on the argument that a small weld on heavy plate cools too fast through the thin throat and is prone to cracking. That table belongs to the code, so look it up rather than guessing. A practical floor of 3 or 4 mm also applies, because anything smaller is hard to deposit reliably whatever the calculation says.
Does this cover a weld loaded in bending or torsion?
No. This is a direct shear check on a single weld run. A weld group loaded out of plane needs the section properties of the group, treating the weld throat as a line of unit thickness, and the resulting shear and normal stresses have to be combined. Bracket welds, lug welds and anything with an eccentric load fall into that category.