Gutters come in 4, 5, 6, and 7-inch widths. Selecting the right width is important. If your gutter trough is too narrow, it will overflow during heavy downpours. Then water could seep in along your exterior walls or foundation. To learn how to choose the right gutter size, you must measure your roof. The square footage of a roof along with its pitch determines appropriate gutter size. Larger roof surfaces collect more rainwater. Steeper roof surfaces allow water to flow rapidly into gutters. A large, steep roof will greatly increase the risk of gutters overflowing.

If you have to climb up on your roof to perform measurements, pay attention to safety. Make sure that your ladder is on stable ground and wear non-skid shoes. You might be able to complete measurements just from the edge of the roof while standing on a ladder.

How to Choose the Right Gutter Size

1. Measure the width and height of each section of roof.
2. If possible, extend your measuring tape up to the peak of the roof while you remain on the ladder. This will produce your height measurement.
3. You can measure the width of roof sections from the ground by measuring the wall.
4. Multiply the width and height for each section. This produces the square footage for each section.
5. After calculating the square footage of each section, add up all sections.
6. You now have the total square footage for the roof.
7. How to choose the right gutter size requires you to find the pitch of the roof.
8. Take a level and mark 12 inches from one end of it. Some levels already include a ruler.
9. Standing on the ladder at the edge of the roof, set one end of the level against the roof. Position it a foot or two up the slope.
10. Hold the level horizontally over the roof until the bubble indicates that the level is level.
11. Measure straight down from the 12-inch mark on the level to the roof.
12. Record the measurement from the bottom edge of the level to the roof.
13. This figure reveals how much the roof rises across 1 foot.
14. Use the result of the pitch measurement to find the correct multiplier.
    1. 0 to 3 inches needs no multiplier.
    2. 4 to 5 inches has a multiplier of 1.05.
    3. 6 to 8 inches has a multiplier of 1.1.
    4. 9 to 11 inches has a multiplier of 1.2.
    5. 12 inches and up need a multiplier of 1.3.
15. Multiply your total roof square footage by the multiplier for your roof’s pitch.
16. If the result is between 5,530 and 7,500, you can use a 5-inch gutter.
17. A result below 5,530 calls for a 4-inch gutter.
18. A result above 7,500 needs a 6 or 7-inch gutter.
19. Now that you know the right gutter size, determine the size of your downspouts.
20. For 5-inch gutters, a 2×3-inch or 3×4-inch downspout should perform well.