Fillet Weld Sizing Technique

Size Is a Measurement — Not a Guess From the Face

Design strength assumes a leg size. Welders often judge “about a quarter” from the face width or the tallest reinforcement. That habit silently undersizes one leg while the other looks huge — and the weak leg governs throat.

For the strength math (0.707, F_w, D/C), use the strength guide. This technique page is the shop how-to: gauge correctly, catch sizing mistakes, and choose intermittent vs continuous deposits when the print allows.

How to Measure / Gauge Actual Leg Size

1. Cool enough to handle safely — hot soft metal “springs” under a gauge and lies about size.
2. Clean slag and spatter at the toes so the gauge seats on plate and weld, not debris.
3. Use a fillet weld gauge (or verified templates) for the nominal size on the print. Seat one blade against each face; both legs must clear for an equal-leg callout.
4. Check both legs independently. A tall vertical face and a short horizontal leg is still undersize.
5. Sample starts, mids, and stops — craters and restarts are where size usually drops.
6. If unequal-leg is specified, gauge each specified size; do not average them into one throat assumption without the detail.

Common Sizing Mistakes

Undersizing is the more dangerous habit on load-bearing joints: capacity falls with the short leg, and inspectors reject the size regardless of your “it held on the last job” story. Oversizing wastes wire and pulls plates — use the next standard increment only when D/C or minimum size requires it, then stop.

When Intermittent vs Continuous Fillet Welds Are Appropriate

Use continuous fillets when:

• The print / WPS requires continuous or seal welds (tank bottoms, weather seals, code callouts).
• Fatigue, vibration, or corrosion needs an unbroken toe line.
• Required capacity needs full length and intermittent spacing cannot deliver enough deposited metal.

Intermittent fillets (staggered or chain) can be appropriate when:

• The detail explicitly shows segment length and pitch (e.g., 3–3, 2–4).
• Stiffness / connection needs are met with less weld volume and less distortion risk.
• You enter total effective deposited length into the calculator — not the overall joint span.

Never invent intermittents to save time on a drawing that shows continuous. When converting print symbols to calculator inputs, multiply number of segments × segment length (and sides) carefully.

When defects already exist, use strength troubleshooting. When you need P and D/C for a leg and length, return to the calculator and the lb/in chart.