How to calculate weld weight
Weld metal weight is the volume of deposited metal times the density of steel. The volume is the weld's cross-sectional area along its length:
Weld metal (kg/m) = Cross-sectional area (mm²) × 7,850 ÷ 1,000,000
For an equal-leg fillet weld of leg size z, the cross-section is a right-angled triangle, so the area is z² ÷ 2 (a small convexity allowance is often added). For a single-V butt weld, the area is the groove cross-section — the root gap rectangle plus the two bevel triangles, with a cap reinforcement allowance.
From deposited metal to consumables
You can't buy exactly the deposited weight — some is lost as stub ends, slag and spatter. Divide by the process deposition efficiency to get the electrode or wire to order:
Consumable required = Deposited weld metal ÷ Efficiency
| Process | Typical deposition efficiency |
|---|---|
| SMAW (stick electrode) | ≈ 0.65 |
| FCAW (flux-cored wire) | ≈ 0.85 |
| TIG / GTAW | ≈ 0.90 |
| MIG / MAG (solid wire) | ≈ 0.95 |
| SAW (submerged arc) | ≈ 0.99 |
Fillet weld metal — quick reference
| Leg size | Weld metal (kg/m) |
|---|---|
| 4 mm | 0.063 |
| 5 mm | 0.098 |
| 6 mm | 0.141 |
| 8 mm | 0.251 |
| 10 mm | 0.393 |
| 12 mm | 0.565 |