What Is the Standard Gutter Size?

When installing new gutters, one of the first things to do is determine the right gutter size. Improperly sized gutters cannot hold the water coming off your roof. As a result, water damage can occur.

The standard gutter size is five inches for seamless gutters. Homeowners with large roofs will want to consider six-inch gutters as they handle almost 50 percent more water than five-inch gutters.

If you want to replace an existing gutter system, you can measure the gutters to determine how wide your new gutters should be. When selecting new gutters, consider the shape and material of your existing gutters.

If, however, you’re installing a gutter system for the first time, you will need to take some roof measurements to figure out what size gutters are the best for your roof. A useful rule of thumb is that the larger your roof surface, and the more it slopes, the larger the gutters required.

Here are some ways to determine the correct gutter size:

Calculate Square Footage of Your Roof’s Surface

First you need to measure the length and width of each area. Multiply the length and width of an area to get its square footage. Add the square footage of every area to get the total soiree footage of your roof.

Calculate the Roof Pitch Factor

The roof pitch factor or roof pitch multiplier indicates the steepness of your roof. To calculate the roof picture factor, you need a two feet level and a tape measure. With one end of the level placed against the roof, measure the distance between the middle of the level and the roof underneath it.

This measurement is known as the 12-inch run. For example, if the gap between the underside and the level’s midpoint is six inches, the roof pitch is 6-in-12.

Here’s a table to help you determine the roof pitch factor

Roof pitch Roof pitch factor
12-in-12 or higher 1.3
9-0in12 to 11-in12 1.2
6-in-12 to 8-in-12 1.1
4-in12 to 5-in-12 1.05
0-in-12 1.0


Once you have determined your roof pitch factor, multiply it with the roof square footage and then with the maximum rainfall intensity-the maximum possible rainfall over a five-minute interval to get the adjusted square footage.

Use the result to determine the right gutter size. For example, if the resulting number is between 5,250 and 7,500, opt for k-style five-inch gutters. If the resulting number is higher, you might need larger six-inch gutters.

Don’t Forget to Determine the Right Downspout Size

Downspouts or downpipes allow the water from gutters to reach the ground without dripping or splashing down the structure of the home. The right-sized gutter downspouts ensure efficient drainage. They drain quickly and can save you money on repairs.

When determining the right downspout size, some important factors to consider are gutter system design, drainage area, gutter outlet capacity, gutter size, gutter style and roof pitch, shape and design.

ARS Roofing and Gutters is one of the most trusted roofing companies in Sonoma County. Our pros have a cost-effective solution to every roofing problem. To schedule gutter installation in Santa Rosa, call 707-584-5900.

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