5-Inch vs 6-Inch Gutters: A Real Sizing Guide for Edina, MN

Quick answer: A 5-inch K-style gutter holds about 1.2 gallons of water per linear foot. A 6-inch K-style holds about 2.0 gallons per linear foot — roughly 67% more capacity for one extra inch of width. That jump isn’t proportional, and it’s the single most useful number in this decision. Whether your Edina home actually needs 6-inch gutters depends on three things: how much roof drains into each gutter run, how steep that roof is, and how fast rain falls here during a summer storm. Most Twin Cities homes were built with 5-inch as a cost default, not as a sizing decision.

One inch of width, 67% more water

Here’s the part that surprises most homeowners: going from a 5-inch gutter to a 6-inch gutter is a 20% increase in width, but it isn’t a 20% increase in capacity. It’s closer to 67%.

That’s because a K-style gutter isn’t a simple tube. It has a flat back, a flat bottom, and a decorative front profile — so widening the trough by an inch adds area across the entire cross-section, not just along one edge. The industry numbers work out to roughly 1.2 gallons per linear foot for a 5-inch K-style and roughly 2.0 gallons per linear foot for a 6-inch.

Across a 40-foot gutter run, that’s the difference between holding about 48 gallons and about 80 gallons at any given moment. During a hard Minnesota downpour, where the question is whether water moves through the system faster than it arrives, that headroom is what separates a gutter that keeps up from one that sheets over the front edge and down your siding.

What the capacity math actually rates

There’s a second number worth knowing, and it’s the one most sizing articles get muddled.

The sheet metal industry’s standard reference tables (published by SMACNA, the Sheet Metal and Air Conditioning Contractors’ National Association) rate gutters by how much roof drainage area they can handle at a given rainfall rate. At a benchmark rate of 4 inches per hour, a 5-inch K-style gutter is rated for roughly 5,520 square feet of drainage area, and a 6-inch K-style for roughly 7,960 square feet.

Notice that’s a 44% increase in rated drainage area — not the 67% increase in trough volume. Both numbers are correct; they’re measuring different things. Volume is how much water the trough can hold. Rated drainage area accounts for flow, pitch, and how quickly water actually clears the system. If you see an article citing 67% more capacity and implying your gutters can now handle 67% more roof, that’s a conflation of two separate figures.

The practical takeaway is simpler than the math: a 6-inch system gives you meaningful margin, but it isn’t a license to ignore how your roof is actually laid out.

Why so many Twin Cities homes have 5-inch gutters that don’t fit the house

Five-inch K-style is the residential default across most of the country, and there’s a straightforward reason for that: it’s what builders install. It meets code, it’s cheaper per foot, and on a modest roof with a simple layout, it’s genuinely adequate.

The problem is that “adequate for a modest roof” gets applied to houses that aren’t modest. In first-ring suburbs like Edina, Hopkins, and St. Louis Park, you’ll find plenty of homes where a 1950s or 1960s builder-grade 5-inch system is still doing the work — except the house has since had a second story added, a dormer built out, or an addition put on the back. Every one of those changes sends more roof area into the same original gutter runs, and nobody re-sized the gutters to match.

Even on unmodified homes, layout matters more than square footage. A gutter that’s technically rated for your roof’s total area can still overflow if:

• Two roof planes converge into one valley that dumps into a single short run. Total area might be fine; the concentration at that one point isn’t.
• An upper roof drains onto a lower roof. The lower gutter is now handling both surfaces, often without anyone accounting for it.
• A long run has only one downspout at the far end. Water has to travel the entire length before it can exit, and the trough fills from the far end backward.
• The roof is steep. Steeper pitches shed water faster and catch more wind-driven rain, which is why sizing tables apply a multiplier for pitch rather than using flat square footage.

That last one matters in Minnesota specifically, because steeper roof pitches are common here — they shed snow better, which is exactly why they were built that way.

The downspout is usually the real bottleneck

You can install the widest gutter on the market and still get overflow if the water has nowhere to go.

A standard 2×3-inch downspout — the one that typically comes with a 5-inch system — has roughly 6 square inches of cross-sectional area. A 3×4-inch downspout, which typically pairs with 6-inch gutters, has roughly 12 square inches. That’s about double the drain opening, and it makes a difference twice over: water exits faster, and debris is far less likely to bridge across the opening and create a clog.

The general rule of thumb is one downspout for every 25 to 35 linear feet of gutter, with 40 feet as the outside maximum between downspouts. If your home has a 50-foot run with a single downspout, adding a second one may do more for your overflow problem than upsizing the gutter would.

How much rain are we actually sizing for?

Sizing tables need a rainfall intensity number, and this is where local matters. Engineers pull that figure from NOAA Atlas 14, the federal precipitation frequency dataset that the Minnesota DNR uses as the state’s reference standard for exactly this kind of design work.

The number that matters for gutters isn’t your annual rainfall total — it’s peak intensity: how hard rain can fall in a short burst. Minnesota’s summers are defined by convective thunderstorms that deliver a lot of water in a compressed window rather than spreading it out over a day. A system sized against a gentle all-day rain and a system sized against a 20-minute August cloudburst are not the same system, even on the same house.

So which one does your home need?

Here’s the honest version, which is less satisfying than a rule of thumb but more useful when thinking of your gutter installation:

5-inch is likely fine if your roof is a simple gable or hip layout, the drainage area per run is modest, the pitch is moderate, and your downspouts are properly spaced. Plenty of Edina homes are correctly served by 5-inch gutters, and upsizing them wouldn’t fix a problem they don’t have.

6-inch is worth serious consideration if you have a large or steep roof, valleys that concentrate flow into one run, an upper roof draining onto a lower one, long runs with limited downspout options, or a documented history of overflow during heavy rain. It’s also worth considering if your home has been added onto since the gutters went up.

If you’re already overflowing, don’t assume gutter width is the answer. Check the downspout count and placement first, then check whether the gutters are pitched correctly toward the outlets, then check for clogs or sag. Upsizing a gutter that’s overflowing because of a blocked downspout solves nothing.

Where ArmourGuard fits into this

This is worth being direct about: a gutter guard only performs as well as the gutter it’s mounted on.

ArmourGuard Leaf Protection keeps debris out of the trough, which preserves the capacity you paid for — a gutter half-full of packed leaves and shingle grit isn’t a 5-inch gutter anymore, functionally speaking. That’s real value. But no guard adds capacity. If a 5-inch system is genuinely undersized for the roof draining into it, it will overflow whether or not it’s guarded, and it will do it on a clean, clear, well-maintained gutter.

That’s why gutter sizing is a question worth settling before adding protection to an existing system, not after. Getting the capacity right first, then keeping it clear with ArmourGuard, is the order that actually works.

FAQ

Are 6-inch gutters worth the extra cost? It depends entirely on whether your roof needs the capacity. On a home with a large or steep roof, converging valleys, or a history of overflow, the added cost is small next to the cost of repeated fascia repair or water reaching the foundation. On a modest, simple roof with well-placed downspouts, upsizing may be spending money on a problem you don’t have.

Can I put 6-inch gutters on just part of my house? Yes, and it’s sometimes the right call. If one section of roof concentrates significantly more water than the rest — a large rear elevation, or a run catching an upper roof — upsizing only that run addresses the actual problem without redoing the entire system. The transition needs to be handled properly at the corner, which is a detail worth discussing during an estimate.

Will bigger gutters stop ice dams? No. Ice dams are caused by heat escaping into the attic, melting snow near the roof ridge, and that meltwater refreezing at the colder eaves. Gutter size doesn’t change that sequence. Larger gutters may hold more ice before the weight becomes a problem, but the fix for ice dams starts in the attic with insulation and air sealing.

How do I know what size gutters I currently have? Measure across the top opening of the trough, from the back edge against the fascia to the front lip. Five inches and six inches are distinguishable by eye once you know what you’re looking for, and the downspout is another clue — a 2×3 downspout almost always means a 5-inch system.

Does gutter material change the capacity? No. Capacity is a function of the profile’s cross-section, not what it’s made from. A 5-inch aluminum K-style and a 5-inch steel K-style hold the same volume. Material affects durability, cost, and appearance rather than how much water the trough carries.