Gutter LF, downspouts, hangers & cost
Enter your building footprint, waste factor, hanger spacing, square feet of roof per downspout, a roof pitch multiplier, and unit prices. The calculator returns gutter linear feet for a gable roof (two eave runs), the hip-roof equivalent shown alongside, the true roof area, the downspout count, hanger count, and a combined cost estimate.
The formulas: gutter LF = 2 × building length × (1 + waste%) for a gable roof, or 2 × (length + width) × (1 + waste%) for a hip roof. Roof area = length × width × pitch multiplier, which converts the flat footprint to the sloped roof surface. Downspouts = ceiling of roof area ÷ the sq-ft-per-downspout setting. Hangers = ceiling of gutter LF ÷ spacing, plus 4.
The pitch multiplier accounts for the slope: a flat footprint of 40 × 30 = 1,200 sq ft becomes about 1,320 sq ft of actual roof surface at the default 1.1 multiplier (roughly a 4/12 pitch). Steeper roofs need larger multipliers — around 1.25 for an 8/12 pitch and 1.4+ for very steep roofs — because the sloped plane is geometrically longer than the footprint.
Downspout sizing uses the industry rule of thumb embedded as the default: one standard 2×3 or 3×4 downspout per 600 sq ft of roof area. You can raise that to 800–1,000 sq ft per downspout if you use oversized 3×4 downspouts, which also clog less.
The table walks the default scenario. With the gable default the calculator shows 2 × 40 × 1.05 = 84 LF of gutter; the hip figure 2 × (40 + 30) × 1.05 = 147 LF appears in the sub-results. At a 1.1 pitch multiplier the roof area is 40 × 30 × 1.1 = 1,320 sq ft, which ÷ 600 gives 3 downspouts (ceil of 2.2). Hangers at 3 ft spacing: ceil(84 ÷ 3) + 4 = 32. At $9 per LF and $90 per downspout the gable cost estimate is 84 × 9 + 3 × 90 = $1,026.
For the hip roof, swap in 147 LF: 147 ÷ 3 ≈ 49, +4 = 53 hangers, and cost becomes 147 × 9 + 270 = $1,593. The calculator shows both figures so you can sanity-check either roof style.
| Input / Output | Gable (default) | Hip roof |
|---|---|---|
| Gutter LF (+5% waste) | 84 LF | 147 LF |
| Roof area (×1.1) | 1,320 sq ft | 1,320 sq ft |
| Downspouts (1 per 600 sq ft) | 3 | 3 |
| Hangers @ 3 ft | 32 | 53 |
| Cost @ $9/LF + $90/ds | $1,026 | $1,593 |
Hanger spacing of 24–36 inches is the manufacturer and code-common standard; use the tighter 24-inch spacing in snow regions where ice loads gutters. Gutter runs should slope about 1/4 inch per 10 feet of run toward the downspout, and runs longer than 40 feet should slope from the middle toward a downspout at each end.
Five-inch K-style gutters handle most residential roofs; step up to 6-inch gutters for steep roofs, long uninterrupted runs, or regions with intense downpours. Larger 3×4 downspouts move substantially more water than 2×3 and are the usual upgrade on new installs.
The most common residential gutter is 5-inch K-style aluminum, which pairs with 2×3 downspouts; 6-inch K-style with 3×4 downspouts is the standard upgrade for large or steep roofs. Aluminum dominates because it resists rust and is light enough for one-person installation. Sectional systems join with connectors and are the DIY default, while seamless gutters are roll-formed on site to exact length, which eliminates most joint leaks — the calculator's linear footage is exactly what a seamless crew will quote from.
Water management doesn't end at the downspout. Discharge should land at least 4–6 feet from the foundation via splash blocks or buried drain pipe, otherwise the roof water you captured simply pools against the basement wall. In freeze climates, add leaf guards and consider heating cables on north-facing runs where ice dams form.
Maintenance is mostly about keeping flow paths open: clean gutters twice a year (spring and fall) and after major storms. Clogged downspouts are the top cause of overflow, which is why the oversized 3×4 size — with the 800–1,000 sq ft per-downspout capacity noted earlier — is worth the small premium on leaf-heavy properties.
How many downspouts do I need?
The common industry rule is one standard downspout per 600 sq ft of roof area — the calculator default. Oversized 3×4 downspouts can serve roughly 800–1,000 sq ft each and resist clogging better.
How do I count gutters on a hip roof?
A hip roof drains on all four sides, so gutter runs are 2 × (length + width). A gable roof only drains on the two eave sides: 2 × length. The calculator shows the hip figure alongside the gable result.
What is a roof pitch multiplier?
It converts flat footprint area to true sloped roof area. The default 1.1 approximates a 4/12 pitch; use about 1.25 for 8/12 and 1.4+ for steep roofs, since steeper planes have more surface than the footprint below them.
How far apart should gutter hangers be?
Every 24–36 inches per manufacturer standards; choose 24 inches in snowy climates. The calculator counts ceil(LF ÷ spacing) + 4 to cover run ends and corners.
How much fall should a gutter have?
About 1/4 inch per 10 feet of run toward the downspout. Runs over 40 feet should be pitched from the center to a downspout at each end.