Weld Fillet Size Calculator — Minimum Size and Load-Based Design per AWS D1.1 and EN 1993-1-8

By /



Fillet weld size must be specified correctly on every engineering drawing — too small risks structural failure; over-specified wastes material, time, and introduces unnecessary residual stress and distortion. This calculator determines the minimum fillet weld leg size per AWS D1.1 (Table 8.8) and EN 1993-1-8 based on plate thickness, and also calculates the required fillet size for a given load based on throat stress.

Weld Fillet Size Calculator







Min. fillet leg size — AWS D1.1 (Table 8.8)—
Min. fillet leg size — EN 1993-1-8 (cl. 4.5.2)—
Required fillet size from load (throat a_req)—
Required fillet leg size from load—
Governing (larger of code min and load req.)—
Max fillet size (must not exceed thinner plate − 1.5mm)—

Fillet throat: a = s × sin(45°) = s / √2 ≈ 0.707 × s (for equal-leg 90° fillet)
EN 1993-1-8 throat stress: τ = F / (a × L × n_welds) ≤ f_vw / γ_M2 (γ_M2 = 1.25)
AWS D1.1 uses design throat = 0.707 × s; allowable shear stress = 0.30 × F_EXX
Min leg size — AWS D1.1 Table 8.8 based on thicker part joined

Arc Welding Processes — Key Parameters Comparison Process Shielding Electrode Deposition Typical Use HI Range SMAW Flux coating Consumable 0.5–3 kg/h General fabrication, site 0.5–3.5 kJ/mm GMAW Gas (Ar/CO₂) Wire feed 2–6 kg/h Structural, automotive 0.3–2.5 kJ/mm FCAW Gas+flux core Cored wire 3–10 kg/h Structural, offshore 0.5–4.0 kJ/mm GTAW Gas (Ar/He) Non-consumable 0.5–2 kg/h Stainless, Ti, root pass 0.1–1.5 kJ/mm SAW Granular flux Wire+flux 5–25 kg/h Heavy plate, pressure vessel 1.0–8.0 kJ/mm PAW Gas plasma Non-consumable 1–4 kg/h Aerospace, precision 0.1–2.0 kJ/mm Relative Deposition Rate SMAW GMAW FCAW SAW Highest © metallurgyzone.com/ — Welding Process Selection Guide
Figure: Comparison of major arc welding processes (SMAW, GMAW, FCAW, GTAW, SAW, PAW) — shielding, deposition rate, heat input range, and typical applications. © metallurgyzone.com/

AWS D1.1 Minimum Fillet Weld Size — Table 8.8

Thicker part joined (mm) Min. fillet leg size (mm) Min. throat (mm)
Up to 6 mm 3 mm 2.1 mm
Over 6 to 12 mm 5 mm 3.5 mm
Over 12 to 19 mm 6 mm 4.2 mm
Over 19 to 38 mm 8 mm 5.7 mm
Over 38 mm 10 mm 7.1 mm

Fillet Weld Geometry and Throat

For a standard equal-leg fillet weld with legs of size s and a joint angle of 90°, the theoretical throat (a) is the perpendicular distance from the root to the face of the weld:

a = s × sin(45°) = s / √2 ≈ 0.707 × s

The design throat in EN 1993-1-8 is the theoretical throat (assuming full root penetration); in AWS D1.1 it is 0.707 × leg size for equal-leg fillets. The throat is the critical dimension governing weld strength — all load capacity calculations use the throat, not the leg.

Maximum Fillet Weld Size

AWS D1.1 and EN 1993-1-8 both specify a maximum fillet weld leg size to prevent burn-through and ensure adequate fusion:

  • Along edges of material 6mm or less thick: equal to plate thickness
  • Along edges of material over 6mm thick: plate thickness minus 1.5mm

If the required fillet size exceeds the maximum, a partial penetration groove weld (PJP) or full penetration weld (CJP) must be specified instead.

References

  • AWS D1.1/D1.1M:2020 Structural Welding Code — Steel. Table 8.8: Minimum Size of Fillet Welds.
  • EN 1993-1-8:2005+A1:2014 Eurocode 3: Design of steel structures — Part 1-8: Design of joints. Clause 4.5.

Leave a Comment

Your email address will not be published. Required fields are marked *

Scroll to Top