Gutter Calculator
Gutter length, downspouts, hangers, and fittings for a house.
Add up every roofline that will carry a gutter.
Roof footprint (plan area), not the sloped surface.
2 x 3 suits most homes; 3 x 4 for large or steep roofs.
Steeper roofs drive more water into the gutter.
Ground to gutter. About 10 ft per story.
You need
120 linear ft
Total run to buy. Sectional gutter comes in 10 ft lengths; seamless is rolled on site in one piece.
- Gutter sections (10 ft)
- 12 sections
- Downspouts
- 4 downspouts
- Downspout stock (10 ft)
- 5 sections
- Hangers
- 60 hangers
- Drop outlets
- 4 outlets
- Elbows
- 12 elbows
- Downspout straps
- 8 straps
- Suggested size
- 5 in K-style
Estimates only. Verify quantities before ordering.
How this is calculated
Effective area = roof plan area x pitch factor. Downspouts = the larger of effective area / area per downspout (about 600 sq ft for 2x3, 1,200 for 3x4) and eave length / 35 ft. Gutter and downspout stock are counted in 10 ft sections. Hangers follow your spacing; 3 elbows and straps every 6 ft are allowed per downspout.
Enter the total length of your eaves and the roof area draining to them, and this calculator returns the full gutter takeoff: linear feet of gutter and 10 ft sections, the number of downspouts, and the hangers, outlets, elbows, and straps that go with them. Measure the eave length along every roofline that will carry a gutter, and use the roof's footprint (plan area), not the sloped surface, for the area.
Downspout count comes from two rules at once, whichever needs more: one downspout for the roof area it can drain, and one at least every 35 feet so each gutter run sheds water in both directions. The gutter size suggestion follows the effective roof area after the pitch adjustment, since a steeper roof throws more water into the gutter during a storm.
Gutter takeoff for common homes
Rows use 2 x 3 downspouts, a medium 4:12 to 5:12 pitch, 24 in hanger spacing, and 10 ft gutter height unless noted. Downspout count applies the area and 35 ft spacing rules together.
| Home | Gutter (ft) | Downspouts | Hangers |
|---|---|---|---|
| Detached garage (24 x 24) | 70 linear ft | 2 downspouts | 35 hangers |
| Small ranch | 120 linear ft | 4 downspouts | 60 hangers |
| Average single story | 150 linear ft | 5 downspouts | 75 hangers |
| Two story | 160 linear ft | 5 downspouts | 80 hangers |
| Large two story | 220 linear ft | 7 downspouts | 110 hangers |
Seamless versus sectional, and gutter material
Sectional gutter comes in 10 ft lengths you join with connectors, which is what makes it DIY-friendly and also where it leaks first: every seam is a future failure point. Seamless gutter is roll-formed to length on site by a contractor from a coil, so a straight run has no joints at all except at corners and outlets. For a long accessible run, sectional aluminum is a reasonable weekend job; for a tall or complex roof, a seamless install is usually worth the quote.
Aluminum is the default: it does not rust, takes a baked finish, and in a 0.027 inch or heavier gauge resists the dents that thin stock picks up from ladders and ice. Steel and copper cost more and are heavier to hang; vinyl is cheap and easy but grows brittle and sags in sun and cold, so it suits mild climates and short runs only. Match the gutter gauge to your ladder habits: thin aluminum on a two-story eave dents the first time someone leans a ladder on it.
Slope, outlets, and where the water goes
A gutter has to slope toward its downspout, about a quarter inch of fall for every 10 feet of run. On a run with a downspout at each end, pitch from a high point in the middle toward both. Too little slope leaves standing water that breeds mosquitoes and freezes; too much looks wrong against the fascia and roofline. Snap a chalk line for the slope rather than eyeballing it, because the eye reads the gutter against the straight eave, not against level.
The downspouts are only half the job. Water dumped at the base of the foundation finds its way into the basement or undermines a slab, so every downspout needs an extension, a splash block, or a buried drain line that carries it at least 4 feet out, and ideally to a point that drains away from the house. Where downspouts tie into a buried line, size the trench gravel and drain pipe for the flow; a 6 inch gutter feeding a pinched drain still backs up.
Common questions
How many downspouts do I need?
Plan one downspout for every 600 square feet of roof a standard 2 x 3 inch downspout drains (about 1,200 for a 3 x 4), and in any case one at least every 30 to 40 feet of gutter so each run sheds in both directions. A long run with a single downspout at one end overflows at the far corner in a hard rain.
Should I use 5 inch or 6 inch gutters?
Five inch K-style handles most homes. Step up to 6 inch for large roofs, steep pitches, valleys that dump into one gutter, or regions with intense rainfall: a 6 inch gutter carries roughly 40 percent more water and pairs with the larger 3 x 4 downspout. When in doubt on a big or steep roof, size up; the cost difference is small next to water getting behind the fascia.
How far apart should gutter hangers be?
Every 24 inches is the standard, tightening to 18 inches in snow country or on long unsupported spans, and 36 inches is the practical maximum. Hidden hangers screwed into the fascia hold far better than old spike-and-ferrule systems, which work loose as the wood expands and contracts.
What fittings does each downspout need?
Figure a drop outlet where it leaves the gutter, about three elbows (two offsets to bring it back to the wall plus one at the base), straps roughly every 6 feet to hold it to the wall, and an extension or splash block to carry water at least 4 feet from the foundation. Keeping roof water away from the foundation is the entire point of the system.
Do I measure the roof slope or the footprint for area?
Use the footprint, the flat plan area the roof covers, then let the pitch setting adjust it. Rain falls vertically, so the horizontal area is what determines the volume a gutter must carry; the pitch factor accounts for wind-driven rain on steeper slopes.