Gutter & Downspout Calculator
Calculate Gutter & Downspout Materials
Estimate gutters, downspouts, and accessories
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Formula
Downspouts = Roof Drainage Area (sq ft) / Drainage Capacity per Downspout (sq ft)
Frequently Asked Questions
How many downspouts do I need?
One downspout per 600 square feet of roof drainage area for 5" gutters, or per 800 sq ft for 6" gutters. Place them at building corners and never more than 40 feet apart along a gutter run.
What size gutters do I need?
5-inch K-style gutters are standard for most residential homes. Use 6-inch gutters for roofs with a steep pitch, large surface area, or in areas with heavy rainfall. Half-round gutters are used for historic or upscale homes.
How much slope should gutters have?
Gutters should slope 1/4 inch per 10 feet toward the downspout. For a 40-foot gutter run, one end should be 1 inch lower than the other.
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