Understanding your result
The headline is the gutter length, with the sections (or seamless runs), corners and end caps in the subtitle. The stats give the sections, corners, end caps and outlets; the breakdown lists every part.
The number to remember is the gutter length: it feeds the hangers calculator and the gutter guard calculator, and each run’s length is what the gutter slope calculator uses for the drop. The number of downspouts comes from the downspout calculator.
How we calculate this
Sections are counted per run, because a 40-foot run cannot borrow the offcut from a 30-foot run around the corner without an extra joint. End caps follow from the topology: each run has two ends, and each corner joins two of them. The eave lengths are the same as the drip edge eaves; measure them once.
The assumptions behind the numbers
| Assumption | Default | Where it comes from |
|---|---|---|
| Runs | two 40 ft eaves | The site’s example gable house |
| Section length | 10 ft | Standard sectional gutter |
| Waste | 5% | Estimating practice |
| Downspouts | 2 | One per run on the example; size them with the downspout calculator |
| Sealant | 1 tube per 10 joints, corners, caps and outlets | Installer practice |
Assumptions last reviewed October 7, 2026.
The calculator does not count the hangers (the hangers calculator does), the downspout pipe and elbows (the extensions calculator does), or gutter on porches unless you add their runs. The gutter sizing guide covers the choice between 5 and 6 inch gutter, the gutter and downspout sizing table gives the capacity of each at your rainfall, and the standard sizes table lists the section, downspout and outlet sizes sold.
Two worked examples
A gable house with sectional gutter
Two 40-foot eaves, no corners, 10-foot sections, two downspouts, 5% waste.
- Length: 80 ft
- Sections: 42 ÷ 10 → 5 per run, 10 in all; joints: 8
- End caps: 2 × 2 − 0 = 4; outlets: 2; sealant: 2 tubes
Eight joints on 80 feet of gutter, each a place to check every autumn.
A hip house with seamless gutter all round
Runs of 40, 40, 30 and 30 feet joined by four outside corners, seamless, four downspouts.
- Length: 140 ft
- End caps: 4 × 2 − 4 × 2 = 0
- Corners: 4; outlets: 4; sealant: 2 tubes
No end caps and no joints: the only seams are at the four corners.
Where to find your inputs
Eave runs. Measure each straight stretch of eave at the drip edge, from end to end.
Corners. Count outside corners (the gutter wraps around the house) and inside corners (it turns into an L).
Downspouts. From the downspout calculator.
Common mistakes
- Measuring the walls. Gutter runs along the eave, which is longer than the wall by the rake overhangs.
- Forgetting end caps. Every open end needs one, left and right are different parts.
- One outlet per house. Each run needs at least one.
- Short sections bridged across corners. Count sections per run.
- No sealant. Every joint, cap and outlet is sealed.
- Ignoring porches. Porch roofs have their own eaves.
Questions people ask
- How many feet of gutter does a house need?
- Add up the eaves, the horizontal edges where water runs off. A 40 by 30 foot gable house has two 40-foot eaves, 80 feet; the same house with a hip roof has eaves on all four sides, 140 feet. Porches and wings add their own eaves.
- How many end caps do I need?
- Two for every run that does not turn a corner into another run. A gable house with two separate runs needs four; a hip house with gutter all the way round, joined by four outside corners, needs none. Each corner joins two ends.
- Seamless or sectional gutters?
- Seamless gutter is formed on site from a coil to the exact length of each run, so it only has joints at corners and ends; sectional gutter comes in 10-foot pieces joined with connectors, and every joint is a possible leak. Seamless costs more to install but less to maintain.
- How many downspouts per gutter run?
- At least one per run, and one per 30 to 40 feet of gutter; more where the roof area draining to the run is large or local rain is intense. The downspout calculator sizes them from roof area and rainfall.
- How much gutter sealant do I need?
- One tube per ten joints, corners, end caps or outlets is a fair rule; the calculator's gable example with eight joints, four end caps and two outlets needs two tubes.
- What size gutter do I need?
- 5-inch K-style for most houses, 6-inch for large or steep roof faces and intense rainfall. The downspout calculator checks the gutter's capacity against the roof area and your local rainfall intensity.