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Weld Size Calculator
Estimate the minimum fillet weld leg size needed to carry a given shear load, based on weld length, allowable shear stress, and a standard safety factor — a starting point before detailed design review.
🔒 This tool runs entirely in your browser. Your files are never uploaded to a server.
Minimum weld leg size
0 mm
Recommended (rounded up)
0 mm
Example shown — this is a preliminary estimate, not a stamped structural calculation.
How it works
- Enter the applied shear load, total weld length, and the base metal's allowable shear stress.
- Set a safety factor to derive a conservative working stress.
- The tool solves the fillet weld throat shear equation for the minimum leg size, then rounds up to a practical 0.5mm increment.
FAQ
What formula does this use?
It uses the standard fillet weld throat shear capacity relationship: load = 0.707 × leg size × weld length × allowable shear stress, where 0.707 accounts for the weld throat being the leg size divided by the square root of 2. Solving for leg size gives the minimum size needed for your load.
Why divide the allowable stress by a safety factor?
The safety factor reduces the material's allowable stress to a more conservative working value, building in margin for load uncertainty, fatigue, and workmanship variation — standard practice in structural and mechanical weld design.
Is this suitable for a final engineering design?
No — treat this as a rough, preliminary estimate only. Real weld design also considers weld type, joint geometry, base metal properties, fatigue loading, and applicable codes (like AWS D1.1), and should be reviewed by a qualified engineer before use in a real structure.
Quick estimate vs. a certified weld design
| Feature | This calculator | Certified weld design |
|---|---|---|
| Fast ballpark leg size for early design | ✓ | ✗ |
| Code-compliant, stamped for construction | ✗ | ✓ |
Use this for a fast preliminary check; get a licensed engineer's sign-off for any load-bearing structure.