Gutter size vs. capacity — how much roof a 5-inch vs 6-inch K-style drains
A gutter’s profile sets its capacity: a 5″ K-style drains ~4,500 sq ft of roof at 1 in/hr, a 6″ ~7,800 (≈1.7×). Size it by roof area ÷ your local rainfall intensity — big or steep roofs need 6″–7″ or more downspouts.
What this diagram shows
Two K-style gutter cross-sections compared. A 5-inch K-style gutter drains about 4,500 square feet of roof at 1 inch per hour of rainfall and ⅛-inch-per-foot slope; a 6-inch K-style drains about 7,800 square feet — roughly 1.7 times as much. A half-round of the same nominal size holds a little less. Size the gutter by the roof area feeding it divided by the local rainfall intensity; steep or large roofs step up to 6 or 7 inch gutters or add more downspouts.
Gutter Calculator
Size gutters & downspouts, count hangers, miters, elbows & straps — per SMACNA roof drainage tables & local rainfall. Free, instant, no signup needed.
