Downspout Calculator

Calculate downspout count, length, and extensions for roof drainage. Get elbows and accessories needed.

🌧️ Downspout Calculator

Results

Downspouts Needed2
Length Each10.0 ft
Total Downspout20.00 lin ft
Elbows4 pcs
Extension Total8.00 lin ft

πŸ’‘ How to Calculate Downspouts

The standard rule is one downspout per 600 square feet of roof area (for 2Γ—3 inch rectangular downspouts) or per 1,200 sq ft (for 3Γ—4 inch). Downspout length equals the wall height plus approximately 1 foot for the top elbow connection from the gutter.

Each downspout requires 2 elbows (one at the top to offset from the gutter and one at the bottom to direct water away). Extensions should carry water at least 4 feet from the foundation. Use splash blocks or underground drain pipes for proper dispersal.

A 1,200 sq ft roof with 9 ft walls: 2 downspouts needed (2Γ—3 size). Length each: 10 ft. Total: 20 lin ft of downspout, 4 elbows, 2 extensions at 4 ft each.

Downspout Calculator FAQ

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