Welding Calculator

A fillet weld is a weld with a roughly triangular cross-section, joining two surfaces at an angle (typically 90 degrees), such as a plate to a flange or two perpendicular plates. It is the most common structural weld type because it requires no special edge preparation.

P = 0.707 x leg x L x tau, where leg is the fillet weld's leg size, L is the weld length, tau is the allowable shear stress for the weld metal, and 0.707 converts leg size to the effective throat thickness for a standard 45-degree equal-leg fillet.

For a standard equal-leg fillet weld, the throat is the shortest distance from the weld root to the hypotenuse of the triangular cross-section. For a 45-45-90 triangle with leg length 'leg', that shortest distance works out to leg divided by the square root of 2, which is leg times 0.707.

This depends on the electrode classification and governing design code, for example AWS D1.1 typically bases allowable weld shear stress on a fraction of the electrode's classified strength (such as E70XX electrodes). Always use the value specified by your applicable structural or mechanical design code rather than an assumed default.

Leg size and weld length are entered in millimeters (mm), and allowable shear stress in megapascals (MPa). The resulting allowable load capacity is shown in kilonewtons (kN).

No, the 0.707 throat factor specifically applies to standard equal-leg (45-degree) fillet welds. An unequal-leg fillet weld has a different throat geometry and requires computing the actual perpendicular distance from the root to the weld face directly, not the simple 0.707 shortcut.

Both weld length and leg size scale the load capacity linearly in this formula, but they have very different practical costs: increasing length adds weld metal proportionally, while increasing leg size adds weld metal roughly with the square of the leg size (since the triangular cross-sectional area scales as leg squared), making longer, smaller welds often more efficient than short, oversized ones.

A fillet weld has a triangular cross-section joining two surfaces without requiring the base metal edges to be shaped, calculated with the 0.707 throat-factor formula used here. A groove weld fills a prepared groove between two plate edges (like a butt weld) and typically achieves full penetration, using a different strength calculation based on the actual weld cross-section.

The very start and end of a weld pass often have irregular, incomplete fusion (craters) before the arc stabilizes and after it is extinguished. Structural codes typically require subtracting an allowance (often twice the weld size) from the total measured weld length to get the effective length used in strength calculations, ensuring the calculated capacity reflects only fully fused weld.

The 0.707 throat-thickness geometry applies to any equal-leg fillet weld regardless of base metal. What changes between steel and aluminum is the allowable shear stress value, which depends on the specific filler metal, base metal, and governing code, so always use the correct allowable shear stress for your actual materials.