It’s vital to get accurate measurements before repairing old gutters or installing new ones. Simply follow our step-by-step instructions.
Measuring Existing Gutters for Repair or Replacement
If you’re doing a simple repair or replacing your gutters with an identical set, you only need to measure your existing gutters.
1. Note the style. Determine the style of gutters you currently have. K-style gutters and half-round gutters are the most common, but some homes have box-style gutters or custom-built fascia gutters.
2. Measure the length. For a full gutter replacement, measure and record the full length of your existing gutters. For repair, measure just the damaged sections.
3. Measure the width. Measure the distance from the side that sits flush against the fascia—the board along the side of your roof’s overhang—to the edge that extends past the roofline. Residential gutters often come in 5- or 6-inch widths, but yours may be a different size.
4. Measure the downspouts. If your gutters have downspouts, record the height of each one. Make sure to account for the angled extension at the bottom.
5. Count the corners, end caps, and elbow pieces. Note how many end caps are right ends and how many are left ends. Count the corner pieces and the number of elbow pieces required for your downspouts.
If you want to upgrade to a different style or larger gutters, you’ll need to know the area of your roof, the roof pitch, and the average amount of rainfall in your area (see below).
Measuring for New Gutter Installation
Measuring for a complete gutter installation is more involved than measuring for replacement because you’ll need to determine the volume of water your gutters can handle and the linear feet needed.
1. Measure the roofline. Measure the length of each section of the roof that will have gutters attached to determine the total length of your gutters.
2. Calculate the drainage area. Measure the length and width of each plane of your roof. Multiply those numbers to calculate the square footage of each section separately, then add all those areas together. The total square footage is the drainage area.
3. Determine roof pitch. Use a level to measure your roof’s vertical rise over a 12-inch horizontal run. This tells you your roof’s pitch, which you can use to determine the roof-pitch factor or multiplier:
- 4:12 or 5:12 = 1.05
- 6:12 to 8:12 = 1.1
- 9:12 to 11:12 = 1.2
- 12:12 or higher = 1.3
4. Determine rainfall intensity. Look up the maximum rainfall intensity for your area on the NOAA website. Enter your location, select “Precipitation Intensity” for the data type, and scroll down to the table. Use the bolded number in the fourth column of the first row (5-minute duration, 10-year recurrence interval).
5. Calculate the adjusted square footage. Multiply your roof’s square footage by the roof pitch factor and rainfall intensity. The product of these three numbers is the adjusted square footage, which you use to determine how wide your gutters need to be. Here is the capacity of four common gutter styles and sizes:
- 5-inch K-style gutters: Up to 5,520 square feet
- 6-inch K-style gutters: Up to 7,960 square feet
- 5-inch half-round gutters: Up to 2,500 square feet
- 6-inch half-round gutters: Up to 3,840 square feet
6. Measure for downspouts. Plan to have one downspout for every 25–30 linear feet of gutters. Measure the distance from your roofline to the ground, plus at least 4 feet for a gutter extension. Multiply this by the number of downspouts needed.
7. Count corners, end caps, and elbows. Determine how many corner pieces, end caps, and downspout elbows you need for your gutter system.