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Complete roofing material takeoff: shingles, underlayment, drip edge, nails, and ice shield. Enter roof area and pitch for full replacement material list.
Calculate soffit and ridge vent area for balanced attic ventilation. Enter attic floor area for IRC 1/150 or 1/300 rules with intake and exhaust balance.
Calculate asphalt shingles needed for your roof. Enter roof area and bundle coverage to get shingle bundles, squares, and waste allowance for reroofing.
Runoff equals rainfall intensity (in/hr) times drainage area (sq ft) times runoff coefficient. Roofs use C near 0.95.
Q = C × i × A (C ≈ 0.95 for roof)Manufacturer capacity tables relate gutter profile to max drainage area at standard rainfall rates.
5″ K-style ≈ 5,520 sq ft @ 1″/hr; 6″ ≈ 7,960 sq ftEach 2×3″ downspout drains roughly 600 sq ft at moderate rainfall. Undersized downspouts overflow gutters even if gutter profile is adequate.
1 downspout per 600–800 sq ft (2×3″); 2×3″ = 600 sq ft maxUpdated: July 2026
At 1″/hr design storm, 5″ K-style gutter handles up to ~5,500 sq ft — adequate with 2 downspouts at 600 sq ft each.
Requires 6″ gutter or dual 5″ runs with 4 downspouts minimum to prevent overflow during peak storms.
Small tributary area ties into existing main gutter — verify combined capacity or add dedicated downspout.
Size residential gutters and downspouts using roof catchment area and local rainfall intensity. Enter tributary roof area and design storm rate to determine minimum gutter profile and number of downspouts needed.