Web sizes, gauge-to-mil conversions and the limiting-height logic that decides whether your wall stands - one page, bookmark it.
Stud size names the web (the wide face): 1-5/8", 2-1/2", 3-5/8", 4", 6" and 8" cover nearly all interior work. 3-5/8" dominates standard partitions; 2-1/2" fits tight chases and furring; 6" appears at plumbing walls, exterior furring and taller runs. C-H studs (2-1/2" and 4") are their own family, built to grip shaftliner in shaft wall systems.
| Legacy Gauge | Mils | Typical Use |
|---|---|---|
| 25 GA | 18 mil | Standard interior non-structural partitions |
| 22 GA | 27 mil | Heavier interior, resilient channel stock |
| 20 GA | 33 mil (30 mil drywall) | Taller partitions, doors, some jambs |
| 18 GA | 43 mil | Structural conditions, heavy jambs |
| 16 GA | 54 mil | Structural, high walls, headers |
Modern drawings increasingly specify mils (the actual steel thickness); legacy gauge persists everywhere else. Watch for "20 GA drywall" (30 mil) versus "20 GA structural" (33 mil) - not the same stud, not the same price.
Every stud size, gauge and spacing combination has a maximum height set by deflection criteria (commonly L/240 for board-finished walls at 5 PSF). A 3-5/8" 25GA stud at 16" o.c. tops out around 13-14 feet at L/240; hit a 16-foot corridor and you need 20GA, 6" studs, or reduced spacing. Manufacturer tables (ClarkDietrich, SCAFCO, Steeler) publish exact values by product.
The estimating trap: drawings that specify one stud for "typical" partitions while sections reveal taller conditions. Our framing takeoffs flag walls that appear to exceed common limiting heights so the fix happens at bid, not at inspection.
Moving from 16" to 24" o.c. cuts stud count by roughly a third - where the assembly and heights permit it. Rated and sound assemblies dictate their own spacing; the listing governs, always.
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