Most homes have 5-inch gutters, and for many roofs that's the right size. But gutters that overflow even when they're clean are often simply too small, or don't have enough downspout capacity, for the roof they serve. Here's how to tell whether 5-inch gutters are enough or 6-inch gutters are worth it.
What the measurement means
Gutter size refers to the width across the top of the gutter. A 5-inch K-style gutter is the residential standard. A 6-inch K-style gutter is wider and deeper and carries substantially more water. Half-round gutters of the same width carry less than K-style, because of their shallower shape.
How much water a roof sheds
One inch of rain falling on 1,000 square feet of roof produces roughly 620 gallons of runoff. A 2,000-square-foot roof sheds about 1,240 gallons from the same inch. What matters most for gutter size, though, is how fast that rain falls. In a heavy downpour, a gutter has to move a lot of water in a short time, and Covina's rain often arrives in concentrated winter storms.
Factors that point to 6-inch gutters
- Large roof sections draining to one gutter run
- Steep roof pitch, which speeds runoff and can make water overshoot a small gutter
- Roof valleys that funnel water from two roof planes into one spot
- Long runs with limited places for downspouts
- Overflow when clean during heavy rain
- Heavy debris from trees, since larger gutters and downspouts clog less
Don't forget the downspouts
Downspouts are often the real bottleneck. A larger 3-by-4-inch downspout drains much faster than the common 2-by-3-inch size, and adding a second downspout to a long run can solve overflow without changing the gutter at all. In many cases, the best fix is a combination: 6-inch gutters with 3-by-4-inch downspouts on the problem sections. See downspout installation and repair.
5-inch vs. 6-inch at a glance
| 5-inch K-style | 6-inch K-style | |
|---|---|---|
| Typical use | Most single-family homes | Large, steep or complex roofs |
| Capacity | Standard | Substantially higher |
| Usual downspout | 2-by-3 inch | 3-by-4 inch |
| Clog resistance | Good | Better, more room for debris |
| Cost | Lower | Higher, more metal and larger downspouts |
| Appearance | Slimmer profile | Bolder profile, suits larger homes |
Can you mix sizes?
Yes. It's common to use 6-inch gutters only on the sections that need them, such as below a valley or along a large rear roof, and 5-inch elsewhere. A good installer explains where and why.
How installers decide
Professionals look at the roof area draining to each run, the roof pitch, valleys, run length and possible downspout locations, along with local rainfall intensity. If your current gutters overflow, tell the contractor where and when. That's the most useful information they can have. For new systems, see gutter installation. For upgrading an existing one, see gutter replacement, and for how size affects price, our gutter cost guide. Local guidance is on our main page about gutter installation in Covina, CA.