Gutter Calculator
Calculate linear feet of gutters, number of downspouts, and materials needed for a complete gutter installation. Works for K-style and half-round gutters in 4-inch, 5-inch, and 6-inch sizes.
Formula & Reference
| Variable | Formula | Units |
|---|---|---|
| Gutter Calculator | Gutter Length = Eave Length + 10% for corners and waste | linear feet + downspouts |
Step-by-Step Examples
120 ft eave length, 1,500 sq ft roof area, 5-inch K-style.
- Gutter: 120 x 1.10 = 132 ft
- Downspouts: 1,500/1,000 = 1.5 -> 2 downspouts
- End caps, elbows, hangers calculated above
200 ft eave, 3,200 sq ft roof, 6-inch K-style.
- Gutter: 200 x 1.10 = 220 ft
- Downspouts: 3,200/1,600 = 2 downspouts (minimum)
- Recommend 3 for redundancy on large roof
40 ft eave, 400 sq ft roof area.
- Gutter: 44 ft
- Downspouts: 400/1,000 = 1 (round up to 1)
- Minimum 1 downspout per gutter run
Real-World Applications
Common Mistakes to Avoid
Undersized downspouts overflow in heavy rain, causing water infiltration at the foundation. Use at least 1 downspout per 1,000 sq ft for 5-inch gutters; add more in high-rainfall areas.
Gutters should slope 1/4 inch per 10 linear feet toward downspouts. Flat gutters pool water and accelerate corrosion and mosquito breeding.
5-inch K-style handles up to 1,000-1,200 sq ft of roof area per downspout section. For large roofs, steep pitches, or high-rainfall climates, upgrade to 6-inch gutters.