Tacoma gets about 40.8 inches of rain a year, and most homes here handle it fine on standard 5-inch K-style gutters. The houses that genuinely need 6-inch have something specific going on: a large roof plane, a steep pitch, too few downspouts, or Douglas fir dropping needles into the trough all winter. Rainfall alone rarely decides it in Pierce County. Here is how the sizing works, and how to tell which house you have.
Start With the Local Math
Tacoma averages 40.8 inches of precipitation a year, a little wetter than Seattle’s 39.3, based on NOAA’s 1991 to 2020 climate normals. November is the wettest month at 6.5 inches.
Look closer at that November figure, though. Those 6.5 inches arrive across roughly 19 rainy days, about a third of an inch a day. Our rain is persistent, not violent. The City of Tacoma’s own surface water manual says the same thing: the 2-year design storm is 2.0 inches over 24 hours, and even a 100-year event is 4.1 inches over 24 hours.
That matters more than any other number here, because gutter capacity is a question of inches per hour, not inches per year. A Gulf Coast thunderstorm drops two inches in an hour; here, two inches takes a day. Which is why 5-inch is honestly enough for a lot of Tacoma homes, provided it is clean, correctly pitched, and has enough downspouts.
Roof Area Is the Real Variable
Gutters are sized to the roof area draining into them, not to the square footage of the house. A 5-inch K-style gutter holds roughly 1.2 gallons per linear foot; a 6-inch holds about 2.0 gallons, close to 65 percent more. At the one-inch-per-hour intensity these charts assume, a 5-inch run is rated for about 5,500 square feet of roof and a 6-inch for about 7,960.
Those numbers look generous until you divide the roof up, because what counts is the area feeding each run. One long gutter catching a wide roof plane with one downspout at the far end is a different job than the same footage split across four runs. It is why two houses of identical size can need different gutters.
Pitch Multiplies the Load
A steeper roof behaves like a bigger roof. The standard adjustment factors:
- Flat to 3/12 pitch: no adjustment
- 4/12 to 5/12: add 5 percent
- 6/12 to 8/12: add 10 percent
- 9/12 to 11/12: add 20 percent
- 12/12 and steeper: add 30 percent
The charts miss a second effect. On a steep roof, water leaves the edge with real momentum and can shoot straight over a narrow trough. That is not an overflow problem, it is an aim problem, and cleaning will never fix it. A 6-inch trough catches what a 5-inch throws past.
Why a Perfectly Clean 5-Inch Gutter Still Overflows
This is the part homeowners find maddening: cleaned in September, spilling over the front edge in November anyway. Usually one of three things is happening.
The trough is losing cross-section to debris. Under Douglas fir and big-leaf maple, needles and seed pods pack into a dense mat. A 5-inch gutter with an inch of packed needles has lost a large share of its capacity, and it did not take long. A 6-inch gutter under the same tree still has usable depth. In Tacoma, debris tolerance is the most common real reason to size up, not rainfall.
The water is concentrated at one point. Roof valleys funnel a large area into a narrow stream that hits the gutter in one spot. That spot overflows while the rest of the run sits half empty.
Or the outlets cannot keep up, which brings us to the part that gets ignored.
Downspout Size: 2×3 vs. 3×4
A gutter is a holding channel. Downspouts are the drain. Get the drain wrong and the size of the channel stops mattering.
A 2×3 inch downspout handles roughly 600 square feet of roof. A 3×4 handles about 1,200, roughly double. One downspout per 40 feet of run is the common minimum, and under heavy tree cover every 30 feet is the better target. Valleys and inside corners usually justify one of their own.
Here is the pairing that matters: 6-inch gutters on 2×3 downspouts create a bottleneck. The trough fills faster than the outlets can empty it and you have paid for capacity you cannot use. Six-inch belongs on 3×4. That is why the two upgrades are quoted together.
A Gutter Sizing Guide for Tacoma Homes
| Roof area feeding one gutter run | Pitch | Typical Tacoma call | Downspouts |
| Under 1,200 sq ft | Up to 6/12 | 5-inch K-style | 2×3, one every 30 to 40 ft |
| 1,200 to 2,500 sq ft | Up to 6/12 | 5-inch is usually fine | 3×4, or more 2×3 outlets |
| 1,200 to 2,500 sq ft | Steeper than 6/12 | 5-inch, or 6-inch under conifers | 3×4 |
| 2,500 to 4,000 sq ft | Any | 6-inch K-style | 3×4, one every 30 ft |
| Over 4,000 sq ft, or commercial | Any | 6-inch, sometimes 7-inch | 3×4 or larger |
Treat this as a starting point, not a verdict. Tree cover, valley placement, and fascia condition can all move a house a row in either direction.
When 5-Inch Is Still the Right Answer
Plenty of Tacoma homes do not need the upgrade, and we would rather tell you that than sell it. A one-story or modest two-story with roof planes under about 1,200 square feet, a moderate pitch, enough downspouts, and no conifer overhead will do fine on 5-inch seamless aluminum for decades.
And 6-inch will not fix the wrong problem. If gutters overflow because the pitch is off, the hangers loosened, or there are three downspouts where there should be six, a wider trough just gives the water a bigger place to sit. Correcting slope, adding outlets, rehanging on hidden hangers, or adding gutter guards is often the better use of the same money. Diagnose first.
One Detail Nobody Local Talks About
One piece of metal matters almost as much as gutter size and almost never comes up in a quote: the gutter apron. It is the flashing that carries water off the roof edge into the trough instead of letting it wick backward onto the fascia. Without it, you can get rot behind a gutter that drains perfectly. It deserves its own post, and we will give it one.
How We Size It
We measure the roof planes, note the pitch, count the valleys, look up at what is growing over the house, and then recommend a size. Often that recommendation is 5-inch, and we say so. For the money side, our guide to what new gutters cost in Tacoma covers what the size decision does to the price.
When you are ready, see our gutter installation service or request a free quote.
Frequently Asked Questions
What Size Gutters Do I Need?
Most homes need 5-inch K-style gutters. Step up to 6-inch when a single gutter run drains more than about 2,500 square feet of roof, the pitch is steeper than 6/12, or heavy conifer debris keeps cutting into the trough’s capacity. The roof area feeding each run matters more than the size of the house.
Are 6-Inch Gutters Worth It for Heavy Rain in Tacoma?
Sometimes, but rainfall intensity is rarely the reason here. Tacoma’s 40.8 inches a year arrive at moderate intensity, spread across many days. The stronger local arguments for 6-inch are large or steep roof planes and constant fir and maple debris, which eats into a 5-inch trough’s usable depth much faster.
What Is the Difference Between 2×3 and 3×4 Downspouts?
A 2×3 downspout drains roughly 600 square feet of roof and a 3×4 drains about 1,200, close to double. A 3×4 also clogs less readily on needles and seed pods. Six-inch gutters should always be paired with 3×4 downspouts, otherwise the outlets bottleneck the extra trough capacity.
Are K-Style Gutters a Good Choice in Tacoma, WA?
Yes, and they are the standard here. K-style holds significantly more water than a half-round of the same nominal width, which is why a 5-inch K-style is rated for roughly twice the roof area of a 5-inch half-round. Half-round is mainly chosen on historic homes for appearance.