Weld Size Calculator

Weld geometry Dimension unit

Fillet leg size

Total weld length

meters

Weld metal density Optional filler deposition efficiency

Weld geometry explained

Equal-leg fillet — idealized right-triangle cross-section, useful for estimating weld metal volume.
Unequal-leg fillet — uses two different leg dimensions for the triangular cross-section.
Square groove — simplified rectangular groove area based on root gap and depth.
Single-V groove — approximates the groove as a triangle plus root-gap rectangle.
Double-V groove — approximates two V-groove halves plus the root-gap contribution.
U-groove — simplified approximation; actual preparation radius and side-wall geometry can change the area.
Plug weld — cylindrical volume based on hole diameter and filled depth.

For production estimating, use the actual weld drawing and joint-preparation dimensions. The geometric profile here is an approximation and does not automatically include penetration, reinforcement or concavity.

This calculator estimates weld-metal geometry and weight. It does not determine whether a weld is structurally adequate, nor does it replace a qualified welding procedure, engineering design or applicable welding code.

Core weld formulas

Equal-leg fillet

Area ≈ leg² ÷ 2

Theoretical throat ≈ 0.707 × leg.

Unequal-leg fillet

Area ≈ leg A × leg B ÷ 2

Weld volume

Volume = cross-sectional area × weld length

Weld weight

Weight = weld volume × material density

Filler requirement

Filler ≈ theoretical weld weight ÷ deposition efficiency

Typical fillet weld reference

3 mm leg

4.5 mm² area

4 mm leg

8 mm² area

5 mm leg

12.5 mm² area

6 mm leg

18 mm² area

8 mm leg

32 mm² area

10 mm leg

50 mm² area

These are idealized equal-leg triangular areas before accounting for actual weld profile.

What changes actual weld weight?

Specified weld size and joint geometry.
Root opening and joint preparation.
Penetration beyond the nominal profile.
Weld reinforcement or cap height.
Concavity or convexity of the finished weld.
Number of passes.
Grinding and rework.
Actual deposited alloy density.
Welding process and deposition efficiency.
Weld length and intermittent-weld pattern.

Frequently Asked Questions

How is a 6 mm fillet weld calculated? For an ideal equal-leg fillet, the cross-sectional area is 6² ÷ 2 = 18 mm². The calculator then multiplies that area by total weld length and material density.

What is the theoretical throat of a fillet weld? For an ideal equal-leg fillet, theoretical throat is approximately 0.707 times the leg size.

Can I calculate weld weight? Yes. Enter the weld dimensions, length and material density. The result gives the estimated deposited weld-metal weight.

Can this calculate filler-metal quantity? Yes. Enter deposition efficiency and the calculator estimates the filler requirement from the theoretical weld-metal weight.

Does a groove weld calculation include reinforcement? The groove modes include an optional cap/reinforcement height as a simplified geometric addition. Actual reinforcement geometry can be more complex.

Can this determine the correct structural weld size? No. Weld sizing for strength requires engineering design, loading, material properties and the applicable welding/design standard.

Are the groove calculations exact? No. They are simplified geometric estimates. Actual joint preparation, root radius, side walls, penetration and reinforcement can change the final weld volume.

Related metal tools

All Metal Tools Metal Welding Cost Calculator Welding Electrode Calculator Welding Wire Consumption Calculator Metal Cut List Optimizer