Gutter Calculator

5 in K-style is the residential default and works for most single-story homes in low to moderate rain climates. Step up to 6 in once your roof drains more than about 5,500 sq ft, or any time you live in a heavy-rain region. A 6 in K-style profile carries roughly 40 percent more water than a 5 in (around 7.4 gallons per minute vs. 5.2 at typical pitch), so the bigger size is also worth it on steep roofs that funnel rain fast or on houses with long, uninterrupted runs.

Seamless gutters are formed on site from one continuous coil of aluminum, so the only joints are at corners and downspouts, which means far fewer leak points. They cost $5 to $10 per linear foot installed. Sectional gutters come in 10 ft snap-together pieces from a home center for $1 to $3 per foot DIY, but every joint is a potential drip. Pick seamless if you can hire a pro with a brake truck; sectional only makes sense for short runs, sheds, or a tight budget.

Plan one downspout per 35 to 40 linear feet of gutter, rounded up, with at least one drain on every run that has a low point. A 140 ft perimeter house needs 4 downspouts. Two-story homes double that count because the upper gutters drain to a separate set of leaders that bypass the lower roof. Add an extra downspout anywhere a long run has a noticeable slope change or a valley dumps a large roof area into one stretch.

Aluminum K-style runs $5 to $8 per linear foot installed and lasts 20 to 30 years. Vinyl is the cheapest at $3 to $5 installed but cracks in cold climates and warps in sun, so plan to replace it in 10 to 15 years. Copper is the high end at $20 to $35 per foot, lasts 50 to 100 years, and develops a green patina that looks at home on historic and craftsman houses. Galvanized steel sits between aluminum and copper at $8 to $15 and lasts 20 to 30 years before rust takes over.

Pick half-round on historic homes (Victorian, Colonial Revival, Tudor, craftsman bungalows) where K-style looks anachronistic. The smooth half-pipe profile matches the trim and fascia detail used before K-style became the US norm in the 1960s. Half-round carries less water per inch of width than K-style, so size up: a 6 in half-round handles roughly the same flow as a 5 in K-style. Material is usually copper or aluminum, and installed cost runs about 30 to 50 percent higher than the equivalent K-style profile.