Calculator
Gutter size calculator: 5-inch or 6-inch?
Enter the roof area that drains into one gutter run, its pitch and whether a valley dumps into it. You get a starting point for gutter size and downspouts before we measure.
This is a planning estimate. We confirm sizes on site before pricing.
How the estimate works
The calculator starts with the flat footprint of the roof area that drains into one run. Steeper roofs catch more wind-driven rain, so pitch raises the effective area. A valley that empties into the run concentrates water at one point, and a metal roof sheds water faster than shingles, so both push the number up again.
That adjusted area is compared with the rule of thumb our crews use: a 5-inch K-style run with 2x3 or 3x4 downspouts handles a normal ranch or two-story roof plane, and once the adjusted area gets large, a 6-inch run with 3x4 downspouts stops the overflow. It is an estimate, not a design, and we confirm it on site.
Measuring roof area from the ground
You do not need to climb. Measure the length of the eave the gutter will hang on and the distance from that eave to the ridge as seen on a plan or a satellite map, and multiply. For a simple gable house, each side of the roof drains to its own run, so use half the house footprint for each side.
When the answer is borderline
If the result sits near the line, go with the larger size on runs that sit over doorways, walkways and window wells, and on any run fed by a valley. Upsizing one problem run often costs far less than replacing the whole system later. Our 6-inch gutter page covers the tradeoffs, and the price guide shows what the upgrade usually adds per foot.
Related: 6-inch seamless gutters, 5-inch K-style gutters, downspout installation and the guide 5-inch or 6-inch gutters.
FAQ
Calculator questions
Why does roof pitch change the gutter size?
Rain rarely falls straight down during a Nebraska storm. A steeper roof presents more surface to wind-driven rain and sends water into the gutter faster, so the same footprint behaves like a bigger roof. Sizing methods add a factor for pitch for that reason, and the calculator does the same.
Do more downspouts fix an overflowing 5-inch gutter?
Often, yes. A run that overflows because water has to travel too far to a single outlet can be fixed by adding an outlet and a 3x4 downspout in the middle. If the run overflows near the outlet itself, or a valley overshoots it, the gutter is probably too small and 6-inch is the better fix.
Are 6-inch gutters too big for a small house?
On a small ranch with short roof planes, 6-inch gutters work but rarely pay for themselves, and the wider face can look heavy on low eaves. We usually keep 5-inch there and size up only the runs that take a valley or sit over an entry.
Is this calculator a quote?
No. It is a planning estimate based on the numbers you enter. We measure every run, look at valleys, outlets and where water lands at the foundation, and then recommend sizes and a price for your house before any work starts.