Gutter Calculator
Calculate how many gutter sections, downspouts, hangers, end caps and elbows you need from the total eave length, with an optional material cost per linear foot.
By CalcBuilt Editorial TeamUpdated September 9, 2026Formulas checked against manufacturer specs, see how we calculate.
Results
- Gutter sections to buy
- 12 sections
- 10 ft sections for 120 ft of gutter, plus 8 seam connectors
- Downspouts
- 4 downspouts
- About one every 35 ft; each needs about 10 ft of downspout per story
- Hangers
- 64 hangers
- One every 24 in plus one extra per run for the ends
- End caps
- 8 end caps
- 2 per run; where two runs meet at a corner, use an inside or outside corner piece instead of 2 end caps
- Elbows
- 12 elbows
- 3 per downspout: 2 to offset from the fascia to the wall, 1 at the bottom to kick water away
Gutter formula
Sections = Total eave length / section length, rounded up
Downspouts = Total eave length / downspout spacing, rounded up
Hangers = Total eave length (in) / hanger spacing + 1 per run
End caps = 2 x runs; Elbows = 3 x downspoutsWorked example
A house with 180 ft of eave in 6 runs, using 10 ft aluminum sections, downspouts every 40 ft and hangers every 24 in: 180 / 10 = 18 sections and 18 - 6 = 12 seam connectors. Downspouts: 180 / 40 = 4.5, so 5. Hangers: 180 x 12 / 24 = 90, plus 6 for the run ends = 96. End caps: 2 x 6 = 12. Elbows: 3 x 5 = 15.
At $8 per linear ft for the gutter itself, 180 ft costs $1,440 before downspouts, hangers and fittings.
Quick reference
| Eave length | Sections | Downspouts | Hangers | Elbows |
|---|---|---|---|---|
| 60 ft | 6 | 2 | 30 | 6 |
| 80 ft | 8 | 3 | 40 | 9 |
| 100 ft | 10 | 3 | 50 | 9 |
| 120 ft | 12 | 4 | 60 | 12 |
| 150 ft | 15 | 5 | 75 | 15 |
| 200 ft | 20 | 6 | 100 | 18 |
| 250 ft | 25 | 8 | 125 | 24 |
How to measure for gutters
Measure each eave that needs a gutter along the fascia and add them up. Count each straight length as a run; a run that turns a corner becomes two runs joined by a corner piece. Divide the total by 10 for sectional gutters and round up. Sections join with slip connectors or seamers, one for each joint, so the number of connectors is sections minus runs.
Seamless gutters are formed on site to the exact length of each run and are priced per linear foot, with no seams to leak. For a run over 40 ft, or with a downspout at each end, the installer pitches the gutter from a high point in the middle toward both ends.
Downspouts, hangers and fittings
Plan a downspout for every 30 to 40 ft of gutter, and for any run over 40 ft put one at each end. Each downspout needs about 10 ft of pipe per story, two elbows at the top to bring it from the fascia back to the wall, one at the bottom to direct water away, and a strap every 10 ft. A splash block or extension at the bottom should carry water at least 4 to 6 ft from the foundation.
Hidden hangers every 24 in are standard, with 18 in in snow country. Every run gets two end caps, or an inside or outside miter where two runs meet at a corner. Buy gutter sealant for every joint, end cap and outlet. Local code may require downspouts to discharge to a storm drain or drywell rather than the street, so check before you plan the bottom elbows.
Key facts
- 5 in K-style is the most common residential gutter; 6 in is used for large or steep roofs and heavy rainfall regions.
- Sectional gutters come in 10 ft lengths. Seamless gutters are roll-formed on site from coil stock in one piece per run, up to 40 ft or more.
- A 2 x 3 in downspout drains about 600 sq ft of roof and a 3 x 4 in downspout about 1,200 sq ft, which is why the rule of thumb is one downspout per 30 to 40 ft of gutter.
- Gutters should slope toward the downspout about 1/4 to 1/2 in for every 10 ft of run.
- Hangers go every 24 in, or every 18 in where snow and ice load the gutter.
Frequently asked questions
How many downspouts do I need?
One for every 30 to 40 ft of gutter, and at least one per run. 120 ft of gutter in four runs needs about 4 downspouts.
How many gutter hangers do I need?
One every 24 in, or 18 in in snow regions, plus one extra per run for the ends. 120 ft of gutter at 24 in spacing with four runs needs about 64 hangers.
Are seamless gutters worth it?
They cost more per foot than sectional gutters but have no seams to leak and are installed in one visit. For long straight runs they are usually the better long-term value.
What size gutter do I need?
5 in K-style handles most homes. Use 6 in when a single gutter run drains more than about 5,000 sq ft of roof, on steep roofs that shed water fast, or in areas with intense rainfall.
Sources and references
Next steps for this project
The usual order for a roofing & siding project. See all roofing & siding calculators.
Results are estimates based on standard formulas and typical product specifications. Confirm quantities with your supplier and local code before ordering.