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Measure along the eaves only — the horizontal edges, not the rakes — and add about 10% for waste. Fit one downspout per 30 to 40 feet of run with a minimum of two per gutter, hangers every 24 inches, and about a quarter inch of fall per 10 feet.
The Gutter Calculator returns the linear feet of gutter, the number of downspouts, and the total project cost for a K-style or half-round gutter system. Enter eave length and roof area and the tool sizes the gutter (5" or 6") and recommends one downspout per 35-40 linear feet. Material options include aluminum (most common), steel, copper, and vinyl. Pair the result with our Soffit & Fascia and Drip Edge calculators for a complete eave-line scope.
Gutter is measured along the eaves — the horizontal edges, not the rakes. What you need beyond the run itself is downspouts, hangers, corners and end caps, all of which follow from the perimeter.
| Eave run | Gutter with 10% waste | Downspouts | Hangers at 24 in | Corners |
|---|---|---|---|---|
| 80 ft | 88 ft | 3 | 44 | 2 |
| 120 ft | 132 ft | 4 | 66 | 3 |
| 160 ft | 176 ft | 5 | 88 | 4 |
| 200 ft | 220 ft | 6 | 111 | 5 |
| 240 ft | 264 ft | 7 | 132 | 6 |
Downspouts are spaced roughly every 30 to 40 feet of run and every gutter needs at least two, however short it is. A single downspout on a long run backs up in heavy rain regardless of the gutter size.
Measure along the eaves only — the horizontal edges — not the rakes. Add about 10% for waste, then work out downspouts at one per 30 to 40 feet of run with a minimum of two per gutter.
One per 30 to 40 feet of gutter run, and never fewer than two on any gutter however short. A single downspout on a long run backs up in heavy rain no matter what size the gutter is.
Every 24 inches as a rule, and closer in snow country where ice loading is a real factor. Fix into the fascia, or into the rafter tails where the fascia is thin.
About a quarter inch of drop for every 10 feet of run, toward the downspout. Too little and it stands; too much and it looks wrong against the fascia line.
Leaking corners? The gutter sealant buying guide matches caulk, tape or coating to the leak.
Clogged downspouts? See the best gutter cleaning tools, including ones that work from the ground.
Rotten fascia behind the gutters? Price it with the fascia board replacement cost calculator.
Adding guards? See the DIY gutter guard buying guide.
Having them fitted rather than DIY? The gutter installation cost calculator prices aluminium, vinyl, steel and copper per foot.
Shopping for someone handy? See our gifts for the handyman.
Gutters ice up every winter? The heat tape calculator works out cable for the gutters and downspouts.
Hanging lights from the gutters? The Christmas lights calculator turns the run into strands.
Need the whole roof at once? The free roofing calculator works out roof area, squares, shingle bundles, underlayment, drip edge, ridge cap and installed cost from one set of measurements.