One-Way Slab / Beam Minimum Thickness for Deflection (ACI 318-19)
The depth that lets a designer skip a deflection calculation entirely: ACI 318-19 Table 7.3.1.1 / 9.3.1.1 gives l/20 simply supported, l/24 one end continuous, l/28 both continuous, l/10 cantilever, times (0.4 + fy/100,000) for non-Grade-60 steel and a lightweight factor. A simply supported 12 ft one-way slab needs 7.2 in; a both-ends-continuous Grade 40 slab only 4.1 in. The serviceability depth the strength tiles assume, for members not supporting damageable partitions. A design aid, not the engineer of record's stamped design.
Formula and source
denom = {simply:20, one-end:24, both-ends:28, cantilever:10}; base = 12 l / denom; kfy = (fy == 60,000) ? 1 : 0.4 + fy/100,000; klw = (wc >= 145) ? 1 : max(1.65 - 0.005 wc, 1.09); hmin = base kfy klw.
The ACI 318-19 Table 7.3.1.1 (one-way slabs) and Table 9.3.1.1 (beams) minimum thickness for deflection control, with the (0.4 + fy/100,000) non-Grade-60 modifier and the lightweight-concrete factor, by name.
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