Weld Size Calculator – Fillet Weld Size IS 800

Calculate required fillet weld size from applied load and weld length per IS 800:2007 design methodology used by structural engineers in India.

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Weld Size Formula (IS 800)

Design Strength = fu / (√3 × 1.25)
Throat = Load / (Weld Length × Design Strength)
Weld Size = Throat / 0.7 (min 3mm)

50kN load, 200mm weld, Fe410:
fwd = 410/(√3×1.25) = 189.4 N/mm²
Throat = 50000/(200×189.4) = 1.32mm
Weld Size = 1.32/0.7 = 1.9mm → use 3mm min

Minimum Weld Sizes (IS 800)

Plate ≤ 10mm

3mm min

Plate 10–20mm

5mm min

Plate 20–32mm

6mm min

Plate > 32mm

8mm min

Frequently Asked Questions

Per IS 800:2007, minimum fillet weld is 3mm for plates up to 10mm, 5mm for 10–20mm, 6mm for 20–32mm, and 8mm for plates over 32mm thick.

The effective throat = 0.7 × weld size for a standard 45° mitre fillet weld. A 6mm weld has 4.2mm throat. The throat is the critical dimension for strength calculations.

Weld Size Calculator – Fillet Weld Size IS 800

Weld Size Formula (IS 800)

Minimum Weld Sizes (IS 800)

Frequently Asked Questions

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