Fillet Weld Throat Calculator
A free, browser-based calculator. Runs entirely in your browser — no sign up, nothing stored.
Enter Values
How to use this calculator
- Enter the fillet weld leg size in mm.
- Optionally add the weld length, and a design shear strength to get a capacity.
- Read the effective throat, throat area and capacity.
How it works
The Fillet Weld Throat Calculator finds the effective throat of an equal-leg fillet weld — the thinnest section that actually carries the load.
For an equal-leg fillet the throat a = 0.707 × leg (the leg times cos 45°). The throat area is a × length, and the shear capacity is the throat area × the design shear strength.
Worked example
6 mm leg, 150 mm long. Throat a = 0.707 × 6 = 4.24 mm; throat area = 4.24 × 150 ≈ 636 mm².
Frequently asked questions
Why 0.707?
For an equal-leg fillet the throat is the perpendicular distance from the weld root to the face — geometrically the leg length × cos 45° ≈ 0.707 × leg.
Can I use these results for final design?
No. These calculators are for first-pass sizing, checking and learning. They assume ideal supports, static loads and elastic behaviour, and they don't apply load factors, member capacity, buckling or connection checks. Always verify against the relevant design code (e.g. AS 4100, AS 1170, Eurocode) and have a qualified engineer sign off structural work.
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Tip: Enter any known values to calculate the remaining results.
All calculations run in your browser. Your inputs are never saved or transmitted.