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MachineCalcs

Fillet Weld Size Calculator

Effective throat and shear capacity of an equal-leg fillet weld from leg size, weld length and electrode strength (E60/E70/E80) — per AISC/AWS 0.30·F_EXX — with an optional load utilization check. Metric and imperial.

Inputs

mm
mm
N

Results

Effective throat(a)
4.242 mm

0.707 × leg size.

Weld capacity(F)
61 470 N

61.47 kN · 6.27 t

Allowable shear × throat × length.

Allowable shear stress(τ)
144.9 MPa

Utilization(u)
—

Enter an applied load to check utilization.

Applied load ÷ capacity (enter a load to check).

  • Throat is 0.707 × the leg size — the 45° throat of an equal-leg fillet. The allowable shear is 0.30 × the electrode tensile strength (AISC/AWS), applied to the throat area.
  • Capacity is the weld metal only. The base metal at the weld must also be checked, and this carries no extra factor of safety beyond the 0.30 allowable (no fatigue).

How it works

An equal-leg fillet weld is designed to fail in shear across its 45° throat, so the effective throat is a = 0.707 · leg. The allowable shear stress is τ = 0.30 · FEXX, where FEXX is the electrode tensile strength (E70 = 483 MPa), per AISC/AWS. The weld capacity is then F = τ · a · L over the weld length L. Enter an applied load and the tool reports the utilization (load ÷ capacity) — at or below 1.0 the weld is within capacity.

Worked example

A 6 mm fillet, 100 mm long, welded with E70: the throat is 0.707 × 6 ≈ 4.24 mm, the allowable shear is 0.30 × 483 ≈ 145 MPa, so the capacity is 145 × 4.24 × 100 ≈ 61,500 N — about 61.5 kN (6.27 tonne) in shear. The calculator returns exactly this.

Frequently asked questions

How do you size a fillet weld?
Work out the throat from the leg size (throat = 0.707 × leg), set the allowable shear at 0.30 × the electrode tensile strength, then the capacity is allowable × throat × weld length. Size the leg so the capacity meets your load; enter the load above to check it.
What is the throat of a fillet weld?
The effective throat is the shortest distance from the weld root to the face. For an equal-leg fillet it is 0.707 × the leg size (sin 45°), because design treats the weld as failing in shear across that 45° plane.
What is the minimum and maximum fillet weld size?
The minimum leg is set by the thicker plate (so the weld cools without cracking — e.g. AWS D1.1 tables). The maximum is the plate thickness for material under 6 mm, and the plate thickness minus 1.5 mm for thicker plate, so the edge stays visible.
What is the difference between E60, E70 and E80 electrodes?
The number is the electrode tensile strength in ksi: E60 = 60 ksi (414 MPa), E70 = 70 ksi (483 MPa), E80 = 80 ksi (552 MPa). The allowable weld shear is 0.30 × that, so E70 gives 144.9 MPa. E70 is the common structural default.
How much load can a fillet weld carry?
Capacity = 0.30 × electrode strength × throat × length. A 6 mm E70 fillet, 100 mm long, carries about 61.5 kN in shear (144.9 MPa × 4.24 mm × 100 mm). Lengthen the weld or increase the leg to carry more.
Does this work in metric and imperial?
Yes — enter the leg, length and load in mm/N or inches/lbf; the throat, capacity and allowable stress convert to your unit system.

Method & assumptions

  • Equal-leg fillet weld loaded in shear; throat = 0.707 × leg.
  • Allowable shear is 0.30 · FEXX per AISC/AWS — there is no extra load or safety factor beyond that, and no fatigue (variable-load) check.
  • The base metal at the weld must also be checked; this sizes the weld metal only.
  • The weld is assumed full-length, continuous and sound (no allowance for craters, undercut or starts/stops).

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