Weld Joint Strength Calculator

Formula

• Fillet throat t = 0.707 × leg size
• Weld area = throat × length
• Stress = force / area (or bending model)
• FoS = allowable stress / weld stress

About this calculator

Part of our Manufacturing Calculators collection. Welding, stamping, punch and die tooling, 3D printing, material weight, and production automation.

How it works

Effective throat area depends on fillet leg size or butt throat thickness and weld length. Weld stress divides applied load by throat area for axial and shear cases. Bending uses a simple beam section model. Compare stress to allowable for factor of safety.

Enter your values in the inputs above and click CALCULATE. Results appear on the right without a page reload. No login and no server upload.

Worked example

8 mm fillet, 100 mm long, 50 kN axial load, allowable 94 MPa.

1. Throat = 0.707 × 8 = 5.66 mm
2. Area = 5.66 × 100 = 566 mm²
3. Stress = 50,000 / 566 = 88.4 MPa
4. FoS = 94 / 88.4 = 1.06 → Marginal

Result: Weld stress 88.4 MPa, factor of safety 1.06 (Marginal).

When to use

• Screening fillet weld size for a given load
• Comparing butt vs fillet throat area
• Quick FoS check before detailed weld design

Limitations

• Simplified bending model for load type 2
• Does not check base metal strength or HAZ
• Allowable stress must match your code (AWS, EN, etc.)

FAQ

Why 0.707 for fillet throat?

For equal leg fillet welds, effective throat is leg × sin(45°) ≈ 0.707 × leg.

What FoS is acceptable?

This tool flags Fail below 1.0, Marginal 1.0–2.0, Pass at 2.0 and above. Follow your applicable weld code.

Is allowable stress yield or ultimate?

Enter the code-allowable weld stress for your design basis — often based on yield with a safety factor.