5-inch, 6-inch or 7-inch gutters: how to tell which size your roof needs

The rule of thumb, and where it breaks

A 5-inch gutter is enough for many houses, as long as each run is short enough and has enough downspouts and the gutter does not overflow in normal rain. You need 6-inch on runs longer than about 40 feet that cannot take two downspouts, on runs over 60 feet, on lower gutters that receive water from an upper roof, and where a valley pours a lot of water onto a short stretch. A 7-inch gutter is for volumes beyond what a 6-inch can carry, for tile or concrete roofs, and where several gutters drain into one. The final answer depends on your roof area, pitch and valleys, which is why it should be decided on site, run by run.

At The Brothers that just do Gutters we install all three sizes, and we size each run separately rather than putting one size on the whole house. The guidance below comes from our own sizing pages and from what our Solutionists check on every visit.

Why one extra inch makes such a difference

Gutter size is the width across the top of the gutter. It sounds like a small step from 5 to 6 inches, but our sizing page notes that a 6-inch gutter, only an inch wider than a 5-inch, can handle about 40 percent more water.

That extra capacity matters most in the moments that do the damage: a heavy downpour when the roof is shedding water faster than a smaller gutter can move it to the downspout. The water has nowhere to go but over the front edge, or over the back edge into the fascia. Many homeowners are now moving to larger gutters for this reason, especially on houses where rainwater keeps overshooting the existing system.

The roof itself sets how hard each gutter has to work. A large roof plane collects more water than a small one, so the run beneath it carries more. A steep pitch sends that water down faster, and in a hard rain it can shoot past the front lip of a narrow gutter instead of dropping into it. Valleys gather water from two planes and pour it onto a few feet of gutter. Our sizing page also notes that the standard residential size varies by region, because climate matters as much as the house. In a place where storms routinely drop heavy rain in a short time, the margin a larger gutter gives you gets used.

When a 5-inch gutter does the job

Five-inch is the most common residential size and the least expensive. Our sizing guidance lists the conditions where it is a good fit. If every run on your house meets them, there is no reason to pay for more.

• Gutter runs under 40 feet with at least one downspout
• Runs over 40 feet that have room for two downspouts
• No overflow during regular, normal rain
• No upper roof or upper gutter draining down into the 5-inch gutter

Signs a run needs 6-inch

Six-inch earns its cost on specific runs, not necessarily on the whole house. These are the situations our sizing page describes where 6-inch is needed. Most of them can be spotted from the ground if you know where to look.

The upper-roof situation is the one homeowners miss most. When a second-story gutter empties its downspout onto the roof below, the lower gutter is carrying its own roof plus the upper one. A 5-inch gutter in that spot overflows at exactly the corner where the upper downspout lands.

• Runs over 40 feet that cannot accommodate two downspouts
• Runs over 60 feet
• Lower gutters that receive water from upper gutters
• Rooflines where a large amount of water concentrates on a small section of gutter
• Inside valleys where water moves quickly and often overflows in heavy rain

Where 7-inch is the right call

Seven-inch is less common on houses, but it solves problems nothing else will. Our 7-inch page lists the cases: when the volume of rainwater is higher than a 6-inch gutter can handle, when several gutters drain into one, when you need overflow protection even in normal rain, and when the roof is tile, concrete shingle or Spanish style, which may require a wider gutter.

Larger sizes are particularly suited to heavy downpours and to houses with gutters at several different heights. If you have a large tile roof or a long back elevation collecting water from several roof planes, ask about 7-inch on those runs specifically. Even larger sizes exist, typically for commercial buildings, and a Solutionist can tell you whether any part of your house needs one. Availability of the largest sizes can vary by location, so it is worth asking early if your house needs them.

A ground-level test you can run before anyone measures

You can learn a lot about your own gutters from the yard. The best time is during a steady, heavy rain, with an umbrella and a notepad. Walk the house slowly and write down what each run is doing. Then, on a dry day, pace off the length of the long runs and count the downspouts on each.

Bring those notes to any estimate visit. They tell the person sizing your system where overflow actually happens, which saves guesswork and makes it easier to judge whether a proposed size change is justified or just an upsell.

• Which runs overflow, and whether it is along the whole length or at one spot
• Corners under valleys where water pours over in a sheet
• Upper-story downspouts emptying onto a lower roof
• Runs longer than about 40 feet with only one downspout
• Downspouts that cannot keep up and back water into the gutter
• Splash marks or washouts directly beneath any overflow point

Downspouts matter as much as gutter size

A gutter only moves water as fast as its downspouts can drain it. A long run with one downspout at the far end forces all the water to travel the full length, and in a hard rain it backs up and spills long before it gets there. Adding a second downspout in the middle of a long run can be as effective as going up a size, and our 5-inch guidance depends on it: runs over 40 feet should have two downspouts. Larger gutters are paired with larger downspouts, so stepping up a size usually improves both halves of the system at once. Sometimes a second downspout simply has nowhere to go, because a door, a patio or a walkway sits under that stretch of eave, and that is exactly when the larger gutter becomes the better fix.

Where the downspout ends matters too. The EPA advises making sure gutters drain rainwater at least 5 feet away from the foundation. A perfectly sized gutter that empties beside the slab still puts the water where you do not want it. I cover discharge and drainage on our local soil in what Dallas storms and clay soil demand from your gutters.

Mixing sizes on one house

You do not have to choose one size for everything. Our sizing page points out that combining two sizes in one system can be a cost-effective way to add capacity exactly where it is needed. A typical example is 5-inch along the front and sides, where runs are short and the roof planes are small, and 6-inch across the back, where a large roof plane and a valley drain into one long run.

Mixed systems can look uniform from the street, since the profile and color match. The savings come from not paying for oversized gutter on runs that never needed it. If you are comparing quotes, a company that proposes mixed sizes with a reason for each run is usually doing more careful work than one that quotes a single size everywhere. My guide to what new seamless gutters cost explains how size fits into the total price.

Will guards or a cleaning fix an undersized gutter?

No. Guards keep debris out, which helps a gutter keep the capacity it has, but they do not add any. A clean 5-inch gutter on a run that needs 6-inch will still overflow in a heavy rain. The same goes for cleaning: if a run overflows even right after it has been cleaned, the problem is size, slope or downspouts, not debris.

It is worth ruling out the simpler causes first, though. A gutter that has lost its pitch holds water and overflows like an undersized one, and a half-blocked downspout does the same. If you are seeing water over the edge and puddles at the slab, start with our guide to overflowing gutters and water at the foundation, which walks through those checks.

How we size your gutters on the visit

Our Solutionists assess the roofline, the pitch, the overhang, the fascia and the valleys before recommending anything. Those five things tell us how much roof drains into each run, how fast it arrives, and where water concentrates. We also note where upper downspouts empty onto lower roofs and where existing downspouts discharge, then recommend a size and downspout layout for each run.

The estimate is free and usually happens within a few days of your call, and you get the recommendation in writing with the reasoning. After approval and a deposit, most projects across Dallas and the surrounding cities are completed within one to two weeks. If you want to know how the job itself runs, read what happens from first call to install day.

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