Gutter guide
5-inch vs. 6-inch gutters: which size your house needs
Most single-family houses do fine with 5-inch K-style gutters. Six-inch gutters are worth it when one run drains a large or steep section of roof, when a roof valley dumps water into one corner, when downspouts can't be added where they're needed, or when you plan to add gutter guards. A 6-inch gutter carries roughly 40 to 50 percent more water than a 5-inch.
5-inch and 6-inch gutters side by side
The "5" and "6" refer to the width across the top of a K-style gutter. The bigger number also means a deeper trough, which is where most of the extra capacity comes from.
| Feature | 5-inch K-style | 6-inch K-style |
|---|---|---|
| Flow area inside the trough | About 7.2 square inches | About 10.5 square inches |
| Relative capacity | Standard for most homes | Roughly 40 to 50 percent more water |
| Usual downspout | 2x3 inch or 3x4 inch | 3x4 inch, to match the extra volume |
| Look on the house | Smaller face; suits most one-story homes | Larger face; in scale with two-story homes and big roofs |
| Cost per foot | Lower | Higher: more metal and larger downspouts |
| With gutter guards | Works with most guard types | More room for water under a guard and in hard rain |
Flow areas are typical published figures for standard K-style profiles; exact numbers vary slightly by manufacturer.
What actually decides the right size
Gutter size gets decided run by run, by how much water reaches each gutter during a heavy rain.
Roof area draining to each run
What matters is the section of roof that sheds water into a particular gutter. A long, deep roof plane on the back of a house may send far more water to one gutter than the small slopes on the front.
Roof pitch
Steeper roofs catch more wind-driven rain on their face and shed it faster. Water coming off a steep roof also has more speed, so it can overshoot a shallow gutter at the outside edge.
Valleys
Where two roof planes meet, they funnel water into one line that hits the gutter at a single point, usually an inside corner. Valleys are the most common reason one corner overflows while the rest of the gutter is fine.
Downspout size and spacing
A gutter can only empty as fast as its downspouts let it. Putting a 6-inch gutter on small 2x3 downspouts creates a bottleneck, and the upgrade is mostly wasted. A common rule of thumb is a downspout for every 30 to 40 feet of gutter, with larger 3x4 downspouts on runs that carry a lot of water. Sometimes adding a downspout to a 5-inch gutter solves the problem without going up a size; our downspouts page covers that.
Length of the run
Long runs collect more water and need enough slope to move it. If a run is long and the only downspout is at the far end, a larger gutter or a second outlet near the middle keeps it from overflowing.
Roof material
Metal roofs shed water quickly and can drop snow in sheets. Many installers lean toward 6-inch gutters and stronger hangers under metal roofs.
Overflow patterns that point to undersized gutters
Clogs and bad slope cause overflow too, so rule those out first. If the gutters are clean, pitched toward the outlets, and still overflow in a heavy rain, size is the likely problem.
- One inside corner overflows every hard rain, below a roof valley
- Water sheets over the front edge along a whole run during a downpour, even when clean
- Water shoots past the outside corners off a steep roof
- The area right around the downspout outlet overflows while the far end of the run is fine
- Splash trenches and staining appear on one side of the house but not others
Fixing undersized gutters
You don't always need to replace the whole house. The usual options, from least to most work:
- Upsize the downspouts on the problem runs
- Add a downspout to split a long run
- Add a valley splash guard at the inside corner below a valley
- Replace only the overloaded runs with 6-inch
- Go to 6-inch on the whole house
Mixing sizes is common. A house can have 6-inch on the runs below big roof planes and valleys and 5-inch everywhere else, with the change made at a corner where it's hard to notice.
Size Lewiston gutters for the downpour
Lewiston averages about 12.9 inches of precipitation a year, based on NOAA's 1991 to 2020 climate normals, which is low. It's tempting to think that means small gutters will do. But gutters get sized for the heaviest few minutes of the heaviest storm. And a dry climate still gets hard downpours.
Here's the math: one inch of rain falling in an hour on 1,000 square feet of roof is about 620 gallons, or roughly 10 gallons every minute, all trying to get through one gutter and its downspouts. A short, intense burst can come down faster than that. How often it rains doesn't change how much water arrives during the burst.
Source for annual precipitation: NOAA 1991 to 2020 climate normals for the Lewiston Nez Perce County Airport.
What that means for a Lewiston house
Size your gutters for the roof above them. On most Lewiston homes with average roof areas and moderate pitch, that still means 5-inch. Where a big back roof plane, a valley, or a steep or metal roof sends a lot of water to one run, 6-inch on that run is the better choice, and it's much cheaper to decide that during installation than to fix overflow later.
The same logic applies to snow. Lewiston averages roughly 10 to 13 inches of snow in a season. A larger, heavier gutter with closer hanger spacing stands up better to snow and ice sitting in it during the short cold snaps.
Half-round, guards, and looks
Half-round gutters
A half-round gutter carries less water than a K-style gutter of the same width, because its trough is shallower. If you want half-round, size it up compared with what you would choose in K-style, or add downspouts. Our copper and half-round page covers that profile.
Planning for gutter guards
Guards cover the top of the gutter, and in hard rain some water can run over them. A 6-inch gutter gives more room for water to get in and keeps capacity in reserve if a little debris builds up underneath. If guards are part of the plan, mention it when sizing; see gutter guards.
Will 6-inch gutters look too big?
On a small one-story house with a narrow fascia, a 6-inch gutter can look heavy. On two-story houses and houses with tall fascia boards, it usually looks in proportion. If appearance matters, using 6-inch only on the back or on the runs that need it is a good compromise.
Cost difference
Six-inch costs more per foot and needs larger downspouts. How much that adds depends on how many runs are upsized. Our gutter cost guide explains how size fits into the overall price. When you're ready to have it measured, start from the gutter installation page.
Quick answers on gutter size
Are 6-inch gutters worth the extra cost?
On runs that take a lot of water, yes: they stop overflow that 5-inch gutters can't handle. On runs below small or gentle roof sections, 5-inch does the job and the extra cost buys nothing.
Can I have 6-inch gutters on only part of my house?
Yes. Mixing sizes is common. The larger size goes on the runs below big roof planes and valleys, with the change in size made at a corner.
Do I need bigger downspouts with 6-inch gutters?
Usually. A 6-inch gutter on small 2x3 downspouts can't drain as fast as it fills. Larger 3x4 downspouts are the normal match for 6-inch gutters.
My gutters overflow. Does that mean they're too small?
Not necessarily. Clogs, a lost slope, and too few downspouts all cause overflow. If clean, properly sloped gutters still overflow in heavy rain, especially at one corner or along one run, size is the likely cause.
What size gutters go with a metal roof?
Metal roofs shed water and snow fast, so 6-inch gutters with strong hangers are often used under them, especially on long or steep roof planes.
Get each run sized for your roof
Call Lewiston Rain Gutters at (208) 858-8002. We measure the roof sections draining to each gutter, look at the valleys and pitch, and recommend 5-inch, 6-inch, or a mix, along with the downspouts to match.
Call (208) 858-8002