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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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.
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Cite this tool
Zerdly. (2026). Weld Volume Calculator. Retrieved from https://www.zerdly.com/tools/weld-volume-calculator/
Tip: Enter any known values to calculate the remaining results.
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