Fillet Weld Size Chart — Minimum and Maximum Sizes per AISC and AWS

Fillet weld size is governed by two limits: a minimum size to ensure adequate heat input into the base metal, and a maximum size to avoid burning through thin material. This reference covers AISC 360-22 Table J2.4 minimum fillet weld sizes, maximum sizes per Table J2.2b, effective throat, weld capacity, and common weld configurations with strength values.

Minimum Fillet Weld Size — AISC 360-22 Table J2.4

Minimum size prevents underbead cracking from rapid quenching of the weld pool in thick base metal. The minimum is based on the thicker of the two parts joined.

Note: For A514 and A517 steels, minimum weld size is governed by preheat and interpass temperature requirements, which may be larger than Table J2.4 values.

Maximum Fillet Weld Size — AISC 360-22 Table J2.2b

Maximum size prevents melting of the base metal edge during welding, which would create a defective weld geometry.

Examples:

• 3/8 in plate edge → max weld = 3/8 − 1/16 = 5/16 in
• 1/2 in plate edge → max weld = 1/2 − 1/16 = 7/16 in
• 3/4 in plate edge → max weld = 3/4 − 1/16 = 11/16 in
• 1/4 in plate edge → max weld = 1/4 in (full plate thickness)

Fillet Weld Effective Throat and Capacity

Effective Throat

For a standard (equal-leg) fillet weld of leg size w:

Effective throat: te = 0.707 × w

Example: 5/16 in fillet weld → te = 0.707 × 0.3125 = 0.221 in

Design Strength per Unit Length (AISC 360-22 Section J2.4)

φRn = φ × 0.6 × FEXX × te × (1 + 0.50 × sin^1.5(θ))

Where:
  φ = 0.75 (LRFD)
  FEXX = electrode tensile strength (ksi)
  te = effective throat (in)
  θ = angle of load to weld axis (0° for longitudinal, 90° for transverse)

For longitudinal welds (θ = 0°, load parallel to weld axis):

• φRn = 0.75 × 0.6 × FEXX × 0.707w = 0.318 × FEXX × w (kip/in per weld)

For transverse welds (θ = 90°, load perpendicular to weld axis):

• φRn = 0.75 × 0.6 × FEXX × 0.707w × 1.50 = 0.477 × FEXX × w (kip/in per weld)

Fillet Weld Capacity Table — E70 Electrode (FEXX = 70 ksi)

The most common structural electrode. E70 matches or exceeds yield strength of A36 and A992.

Longitudinal Shear (θ = 0°): φrn = 0.318 × 70 × w = 22.3w kip/in

For two-sided welds (both sides of a connection), multiply by 2.

Fillet Weld Capacity Table — E80 and E100 Electrodes

Higher-strength electrodes for A572 Gr60+, A514, and high-strength steels.

Common Electrode Selection

AWS D1.1 prequalified filler metals: E70 electrodes (E7018-H4R for SMAW, E70T-1 for FCAW, ER70S-6 for GMAW) are prequalified for A36, A572 Gr50, and A992. Always verify prequalification status in AWS D1.1 Table 4.5.

Metric Fillet Weld Sizes

For AS/NZS 1554 and EN 1993-1-8 design:

Minimum Weld Sizes (AS/NZS 1554.1)

Design Capacity per Unit Length (AS/NZS 1554, SP category welds)

φRw = φ × 0.6 × fu × tt × kr

Where: φ = 0.8 (SP welds), fu = electrode tensile strength, tt = throat thickness = 0.707 × weld size, kr = 1.0 for standard joints

Frequently Asked Questions

What weld size should I use for a 3/8 in gusset plate? The thicker joined part governs minimum size. For 3/8 in ≤ 1/2 in: minimum weld = 3/16 in. Maximum weld at the 3/8 in plate edge = 3/8 − 1/16 = 5/16 in. Typical design choice: 5/16 in fillet weld (E70), which gives 6.96 kip/in longitudinal capacity.

When does transverse weld strength apply? Transverse welds (load perpendicular to weld axis) are 1.5× stronger than longitudinal welds due to favorable stress distribution on the throat. Use the transverse multiplier when the weld is loaded perpendicular to its length — common in flange-to-web welds under bending load. For mixed loading, use the vector sum method per AISC 360 Eq. J2-6a/b.

Can I use a smaller weld than the minimum? No. Minimum weld sizes in Table J2.4 are mandatory per AISC 360 Section J2.2b. Undersized welds may have improper fusion due to insufficient heat input relative to the base metal heat sink. Even if the calculated capacity is adequate, the minimum size governs.

Is a 1/4 in fillet weld the minimum for all connections? No. For material thicker than 3/4 in, the minimum is 5/16 in. For material up to 1/4 in, the minimum is 1/8 in. The thicker joined part determines which minimum applies, regardless of the thinner part.

What does "weld all around" mean? A continuous weld applied to the full perimeter of a connection element (e.g., a pipe or tube to a base plate). Symbolized on drawings by a small circle at the weld symbol elbow. Required when the weld must seal against moisture intrusion or when eccentric loads could peel open an incomplete weld.

How do I calculate the required weld size to transfer a 60-kip shear force using E70 fillet welds? Assume two longitudinal fillet welds (one each side) of length L inches. Longitudinal capacity per inch per side: φrn = 22.3w kip/in (where w is the weld leg in inches). Total capacity = 2 × 22.3w × L. For a 10 in weld length each side: required w = 60 / (2 × 22.3 × 10) = 0.135 in → use 3/16 in (next standard increment above 1/8 in). Always check minimum size: for a 3/8 in plate joined to a 1/2 in plate, minimum is 3/16 in (thicker part = 1/2 in). Maximum at 3/8 in edge = 5/16 in. The 3/16 in weld satisfies all limits.

What is the maximum weld size on a 1/2 in plate edge, and what happens if I exceed it? The maximum fillet weld size along a 1/2 in plate edge is 1/2 − 1/16 = 7/16 in, per AISC 360 Table J2.2b. Exceeding this limit causes the weld to undercut or burn through the plate edge, creating an unacceptable weld profile with reduced effective throat. The resulting defect would require gouging and rewelding. In practice, most fabricators stop at t − 1/16 in automatically when welding along an edge, since the flat edge provides natural dimensional control.

Run This Calculation

→ Welded Connections Calculator — fillet and groove weld capacity per AISC 360, AS 4100, and EN 1993, with directional strength increase for transverse welds.

→ Gusset Plate Calculator — gusset plate and weld group design including weld size selection and capacity checks.

Related pages

• Minimum Fillet Weld Size Reference — AISC J2.4 and AS 4100 minimum size tables with code comparisons
• Beam Capacity Calculator — includes weld capacity check for moment connections
• Welded Connections Calculator — fillet and groove weld capacity per AISC 360, AS 4100, EN 1993
• Gusset Plate Calculator — weld group design and size selection for braced frame connections
• Steel Connection Types — bolted vs. welded connection selection
• ASTM A36 Steel — base metal properties for A36 welded connections
• HSS Connection Design — special weld requirements for HSS tube connections
• Steel Grades Reference — electrode matching table for A36, A572, A992, A514
• Steel Connection Design
• Weld Symbol Chart
• Bolt Torque Chart
• AWS weld symbol generator
• Weld size selection guide

Weld capacities are LRFD (φ = 0.75) per AISC 360-22. Always verify electrode pre-qualification status per AWS D1.1 for the specific base metal and joint configuration. Weld quality inspection (visual, PT, MT, UT) must meet AWS D1.1 Chapter 8 requirements.

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