Going Down the Downspout: How to Choose the Right Downspout Sizes

An image of downspout sizes.

Gutter downspouts are an important part of your gutter system. But did you know the downspout sizes are important? Here's how to choose the best size.

3 min read

In 2019, the contiguous U.S. saw an average of nearly 35 inches of rainfall, making it one of the wettest years on record.

Rain is an important part of our ecosystem. Without it, we wouldn't have healthy crops or enough water to drink.

Unfortunately, you can have too much of a good thing. In the case of rain, too much of it can damage your home's foundation and lead to flooding in your yard.

The good news is, a gutter drainage system with downspouts will send the water away from your home. Read on to learn about downspout sizes and how to choose the right size for your home.

Why Do Downspout Sizes Matter?

Your home's gutters catch the rainfall from your roof and the downspouts drain the water from the gutters. When the gutters and downspouts are too small, the gutters can overflow during heavy rain.

It can lead to leaks in your basement and water damage on your siding. Worst case scenario, it can cause foundation issues which can cost as much as $30,000 to fix.

Gutter downspout sizes are measured by their diameter. The larger the diameter, the more water the downspout can handle.

Standard Downspout Sizes

Downspouts and gutters generally come in two styles: K-style and round. You should stick to the same style for both your gutters and your downspouts.

K-style downspouts are rectangular and come in sizes of 2x3 or 3x4 inches in diameter. You can find round downspouts in diameters that range from 3 to 6 inches.

Rectangular downspout sizes are similar to the K-style, but they're also available in a larger 4x5 inch diameter.

Know the Size of Your Gutters

When you're sizing downspouts, you'll need to know the watershed area of your roof and the maximum rainfall intensity for your area.

The good news is, if you already have gutters, this figure has already been calculated. You can just go off of the size and style of gutters you have. Gutter and downspout capacity are both shown in square footage amounts.

Most homes have gutter sizes that are either 5 or 6 inches in diameter.

K-style gutters in the 5-inch size can handle about 5,500 square feet of water, whereas the 6-inch size can handle almost 8,000. Round gutters in the 5-inch size can handle about 2,500 square feet and the 6-inch size can handle nearly 4,000.

Choosing the Right Downspout Dimensions

Generally speaking, 5-inch K-style gutters will need 2x3-inch downspouts and 6-inch will need 3x4.

Keep in mind that these are only guidelines. If it rains a lot in your area or your roof has a high pitch, you may need larger downspouts. Instead of using larger downspouts, you can also add more downspouts to boost your drainage capacity.

Now you're ready to either install your own downspouts or know what to ask for when talking to a roofing and gutter specialist.

Update Your Downspouts Today

If your drainage system isn't working as it should, it might be time to upgrade your downspouts. Once you know about downspout sizes, you'll know how to best protect your home from water damage.

To get more home maintenance tips, keep scrolling through our blog, and check out this article.

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