Gutter calculator

Every line shows the quantity to buy and how StudSheet got it: the spacing, the waste and the package size, so you can check it before the supply house or the quote.

In Canada (25.60 m of gutter, 4 downspouts)

Set to Canada, the Sheet works the job out again for Ontario: metric sizes, bag sizes, the frost depth and the code notes. It doesn't just convert feet to meters. The first lines:

• 4 lengths, Aluminum K-style gutter, 127 mm: 2 runs of 12.80 m of eaves (25.60 m) in 4.88 m and 3.05 m lengths with the least left over, + 1 spare (one per 4 joints) for mistakes.
• 3 lengths, Aluminum K-style gutter, 127 mm: The rest of the runs, in 3.05 m lengths, + 1 spare.
• 4 connectors, Gutter connectors (slip joints): One at each joint between lengths, sealed from the inside.
• 34 hangers, Hidden gutter hangers with screws: Every 813 mm (UIUC: no more than 813 mm for aluminum) along 25.60 m, + one at each run’s end; screwed into the rafter tails.
• 4 caps, Gutter end caps: Two per run, crimped on and sealed.
• 4 outlets, Gutter drop outlets: One per downspout.

1. Take down the old gutters and downspouts: unscrew or pry out the hangers, lower each run with a helper, and scrap the aluminum.
2. Inspect the fascia and drip edge; replace soft fascia boards before hanging anything.
3. Mark the outlets (4 downspouts) and snap a slope line: ¼″ drop per 10 ft toward each outlet; runs over 40 ft slope from the middle to both ends.
4. Assemble the runs on sawhorses: cut the lengths, join them with connectors, add the end caps and cut in the outlets; seal every joint from the inside.
5. Hang: a hanger every 32″ screwed through the fascia into the rafter tails, the gutter’s back up under the drip edge, following the slope line.
6. Downspouts: two elbows out from each outlet to the wall, pipe down, a strap every 6–8 ft, a bottom elbow and an extension that sends the water 4–6 ft from the foundation.
7. Seal and test: run a hose at the high end of each run; watch for drips at the joints and water standing in the gutter.

Must-have tools first, then the ones that help and the ones to rent for the day.

Mistakes that cost a callback or a second trip

• Hanging the gutter level, or the wrong way: Water stands and rots the fascia. Snap a line: ¼″ drop per 10 ft toward the outlet.
• Hangers into the fascia only: A full gutter pulls them out. Every hanger finds a rafter tail behind the fascia.
• Joints sealed on the outside: Water runs under the bead. Seal from the inside, over clean, dry metal.
• Downspouts dumping at the foundation: It ends up in the basement. An extension or splash block carries it 4–6 ft away.
• A ladder resting on the gutter: It crushes the gutter and slides. Use a standoff, and keep the ladder 1 out for every 4 up.
• Outlets where nobody wants water: Over a walk, a driveway or the door. Place outlets where an extension can carry the water away.

What the calculator assumes

• A gable roof over 40′ × 30′ with 12″ overhangs at 6/12: 1503 sq ft of roof draining to 2 runs of 42 ft of eaves.
• Size (University of Illinois Small Homes Council): 5″ with downspouts under 30 ft apart, 9/12 or less and up to 30 sq ft of roof per foot of gutter; otherwise 6″. A downspout drains about 100 sq ft of roof per square inch of its opening: a 2×3 about 600 sq ft, a 3×4 about 1,200; one per 30 ft of 5″ gutter at least.
• Hangers every 32″ (aluminum, UIUC), 24″ where snow and ice stay; slope ¼″ drop per 10 ft (the UIUC allows level, but a little fall drains it dry).
• Downspouts: eaves about 10 ft up + about 2 ft of jog, in 10 ft lengths; 3 elbows, 2 straps per length and an extension each.
• Sealant: a tube per about 6 joints, caps, outlets and corners.

The Sheet sets its code notes for the job's state or province. These are New Jersey's and Ontario's; the code reference has more. Always confirm with your building department.

• Sizing: the University of Illinois rule: 5″ gutters work while downspouts are under 30 ft apart, the pitch is 9/12 or less and each run drains no more than 30 sq ft of roof per foot of gutter; otherwise 6″. A downspout drains about 100 sq ft of roof per square inch of its opening: a 2×3 about 600 sq ft, a 3×4 about 1,200.
• Under the drip edge: The gutter’s back goes up under the drip edge, so water off the shingles lands in it. No drip edge? The Roof Sheet counts it; a strip of gutter apron does the job on an old roof.
• Codes: The IRC (R801.3) asks for a way to carry roof water at least 5 ft from the foundation only where soils are expansive or collapsible; many towns want downspouts kept off the sewer and the neighbor’s lot. Ask your town’s construction office.
• No permit for gutters in New Jersey: Repairing, replacing or installing exterior gutters and leaders is ordinary maintenance in New Jersey: no permit (N.J.A.C. 5:23-2.7).
• Usually no permit: Gutters and downspouts usually need no building permit; ask your municipality’s building department where downspouts may drain. Confirm with your building department.

What materials do I need to install gutters and downspouts?

For the worked example, a 84′ of gutter, 4 downspouts, the Sheet counts 12 lines with waste included, starting with aluminum K-style gutter, 5″ (4 lengths), aluminum K-style gutter, 5″ (3 lengths), gutter connectors (slip joints) (4 connectors), hidden gutter hangers with screws (34 hangers). Each line's math is in the table above. Put in your own sizes in the gutters calculator and every line is counted again.

How long does it take to install gutters and downspouts, and can I do it myself?

About 24 to 38 hours for the worked example, in 7 steps. StudSheet stamps it DIY OK: you can do this.

What tools do I need to install gutters and downspouts?

17 in all. The must-haves start with chalk line, 4-ft level, tape measure (25 ft), cordless drill/driver, aviation snips, hacksaw. On the Sheet you mark each one as owned, to buy or to rent.

Stuck while you install gutters and downspouts? Ask in the Gutters and downspouts group of the StudSheet community with this Sheet attached. Homeowners who've done it and verified pros answer, and anyone can read it.

• Roofing, siding and gutters for contractors: run this takeoff at your own prices, send the estimate, and get it signed and the deposit paid.
• Shingle roof (40′ × 30′ house, 6/12 roof): Squares, bundles, underlayment, ice barrier, drip edge, flashing, vents and nails for an asphalt shingle roof.
• Install or replace siding (40′ × 25′ house, 2 stories): Squares of vinyl, fiber-cement or engineered-wood lap siding for your house, with house wrap, starter, J-channel, corners, trim and nails — from the same answers as the exterior paint Sheet.
• All 45 Sheets, across 16 trades.
• Code reference: frost depths, guard heights, stairs, retaining walls.