Box Gutter Design

Logic Explained

This calculator determines the required gutter size based on the Tributary Area per Downspout, rather than the entire roof at once.

• Trib Area per DS: (Roof Area / Total Run Length) × Spacing.
• GPM per DS: Trib Area × Intensity × 0.0104.
• Required Depth: Based on the cross-sectional area needed to move that GPM horizontally to the outlet.

Downspout Capacities

• 4x4: ~180 GPM
• 4x5: ~225 GPM
• 5x5: ~280 GPM
• 6" Round: ~320 GPM