Fillet Weld Size Limits and Effective Throat (AISC 360 J2.2b)
What size the code allows before the strength calc even applies.
Example
You enter
- Part 1 thickness (in) 0.5
- Part 2 thickness (in) 0.375
- Chosen weld leg w (in, 0 to skip) 0.25
You get
- Min leg (in) 0.1875
- Max leg (in) 0.3125
- Effective throat te = 0.707 w 0.177 in
- Minimum length 4w 1.00 in
Details, formula, and sources
The Table J2.4 minimum leg from the THINNER part joined (so the weld cools slowly enough not to crack), the J2.2b maximum along an edge (full thickness under 1/4 in, thickness minus 1/16 at or over - so the edge is not melted away), the equal-leg throat 0.707 w, and the 4w minimum length. A 1/2 to 3/8 in joint takes a 3/16-to-5/16 window, and a chosen 1/4 in weld carries a 0.177 in throat. The numbers a WPS is written to; a fillet-weld strength check assumes you already picked them. A fabrication aid; AWS D1.1 and the engineer govern.
min_leg from Table J2.4 by the thinner part (1/8 to 5/16 in brackets); max_leg = t (t < 1/4 in) or t - 1/16 (t >= 1/4 in) along an edge; te = 0.707 w; min length = 4 w.
The AISC 360-22 Table J2.4 minimum fillet-weld size, the J2.2b maximum size along an edge, the equal-leg effective throat, and the four-times-leg minimum length, by name.
AISC 360 is free to read at aisc.org (Specification for Structural Steel Buildings); Table J2.4 and the J2.2b limits are in the published specification.
Estimate. AHJ and licensed professional govern.
Field names used by the API: t1_in, t2_in, w_in, min_leg_in, max_leg_in, te_in, min_len_in
- Minimum leg set by the THINNER part joined so the weld does not quench-crack: 1/8 / 3/16 / 1/4 / 5/16 in by thickness bracketAISC 360-22 Table J2.4
- Maximum along an edge the full thickness under 1/4 in; thickness minus 1/16 in at or over, so the edge is not melted awayAISC 360-22 J2.2b
- Geometry equal-leg throat 0.707 w and a minimum load-carrying length of 4 legsAISC 360-22 J2.2a/J2.2b