Weld Volume Calculator

An equal-leg fillet weld is idealised as a right-angled triangle sitting in the corner between two plates.

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Enter Values

Weld leg size

Weld length

Deposited metal density (kg/m³, optional)

Enter your values and press Calculate to see results.

Before you rely on this: First-pass guide only. Verify safety-critical or regulated work against the relevant standards, your project requirements and a qualified professional.

How to use this calculator

Enter the fillet weld leg size in mm (the leg is the length of each side of the weld triangle along the plate faces).
Enter the total weld length in mm — sum the runs if there are several identical welds.
Leave density at the default 7,850 kg/m³ for carbon steel, or override it for stainless (~8,000) or aluminium (~2,700). Read off the cross-section area, volume and deposited mass.

How it works

An equal-leg fillet weld is idealised as a right-angled triangle sitting in the corner between two plates. With a leg size z, the two perpendicular sides both equal z, so the triangular cross-section area is z² / 2. Multiplying that area by the weld length gives the deposited weld volume: V = (z² / 2) × L. This is the same triangle whose throat (z × 0.707) is used for strength — here we want the enclosed area, not the throat.

Deposited weld metal mass is the volume times the metal's density: m = V × ρ. Working in consistent units, a volume in mm³ is multiplied by 1e-9 to reach m³, then by the density in kg/m³ (7,850 for carbon steel). The result is the theoretical fused-metal weight. It deliberately ignores weld convexity/reinforcement, root gaps, and deposition losses, so treat it as a clean lower-bound estimate for consumable planning — not a final design or procurement figure.

Worked example

6 mm fillet weld, 500 mm long, in steel. A single equal-leg fillet weld has a 6 mm leg and runs 500 mm. Cross-section area = 6² / 2 = 18 mm². Volume = 18 × 500 = 9,000 mm³ = 9 cm³. Deposited weld metal = 9,000 mm³ × 1e-9 × 7,850 kg/m³ = 0.0707 kg (about 70.65 g). Remember this is the theoretical fused metal only — the filler wire or electrode you actually consume is higher once deposition efficiency and spatter are accounted for.

Common mistakes

Confusing leg size with throat thickness. This tool wants the LEG (side) of the fillet; the design throat is 0.707 × leg. Entering the throat where the leg belongs understates the volume by about half.
Mixing units. Leg and length must both be in mm here. Entering length in metres (e.g. 0.5 instead of 500) gives a volume 1,000× too small.
Assuming the deposited mass equals the filler wire or electrode you buy. Deposition efficiency (SMAW ~60–65%, MIG ~90–98%) and spatter mean actual consumables are higher — divide the deposited mass by the process efficiency to size purchases.

Frequently asked questions

Does this include weld reinforcement or convexity?

No. It models a flat-faced equal-leg fillet as a perfect right triangle (area = leg² / 2). Real welds usually have a slightly convex face, so actual deposited metal is a little higher. For rough consumable estimates the difference is small; for tight material budgeting add a convexity allowance.

How do I get the actual filler wire or electrode I need to buy?

Divide the deposited weld-metal mass by the process deposition efficiency: roughly 0.60–0.65 for stick (SMAW), 0.90–0.98 for MIG/MAG, and 0.85–0.90 for flux-cored. For the 70.65 g example above, MIG at 0.95 needs about 74 g of wire; stick at 0.62 needs about 114 g of electrode.

Can I use this for a butt or groove weld?

Not directly — this assumes a triangular fillet cross-section. A groove weld's area depends on its bevel angle, root gap and reinforcement, so its cross-section must be computed from the joint geometry before multiplying by length.

Tip: Enter any known values to calculate the remaining results.

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