Gutter & Downspout Sizing Calculator
Calculate seamless gutter size (5-inch vs 6-inch K-style), downspout quantity, hidden hanger spacing, and slope drainage pitch per roof square footage.
Calculated Results
Frequently Asked Questions
When should you choose 6-inch gutters over standard 5-inch gutters?
Standard 5-inch K-style gutters handle smaller roofs in mild climates. 6-inch gutters hold 40% more water volume and are strongly recommended for steep roof pitches (8:12+), large surface areas, metal roofs, and regions prone to heavy torrential thunderstorms.
How many downspouts are required per linear foot of gutter?
Roofing industry standards recommend one downspout for every 30 to 40 linear feet of gutter run. Adding an extra downspout prevents overflow at corner miters during peak flash downpours.
What is the correct pitch slope for rain gutters?
Gutters should slope downward toward the downspout at a rate of 1/4-inch to 1/2-inch of vertical drop for every 10 linear feet of run. Insufficient slope causes standing stagnant water; too much slope looks noticeably crooked on the fascia board.
Why are 3x4-inch downspouts superior to 2x3-inch downspouts?
A 3x4-inch downspout has a cross-sectional area of 12 square inches, which is more than double a 2x3-inch downspout (6 sq in). This dramatically reduces clogs from twigs, pine needles, and maple seeds.