What size gutters do I need?

Most residential homes use 5-inch K-style gutters. Homes with large roof areas or steep pitches in high-rainfall regions may need 6-inch gutters to handle the increased water volume.

How do I calculate gutter length?

Measure the total length of all roof edges (eaves) where you plan to install gutters. Add 5-10% extra for overlaps at seams, corners, and waste from cutting.

What is the difference between 5-inch and 6-inch gutters?

A 5-inch gutter handles about 5,520 square feet of roof area in moderate rainfall. A 6-inch gutter handles roughly 40% more water, making it the better choice for large roofs or areas with heavy rainfall.

How many downspouts do I need?

Place one downspout for every 20 to 30 linear feet of gutter, and at least one per gutter run. Each downspout should drain no more than about 1,200 square feet of roof area.

Gutters & Downspout Calculator

Calculate the gutters, downspouts, hangers, end caps, and miters needed for your roof. Size your gutter system based on roof drainage area and local rainfall intensity.

Roof Drainage Area (sq ft)

Rainfall Intensity (in/hr)

Gutter Size

Total Gutter Run (linear feet)

Number of Corners

Number of Gutter Run Ends

Materials List

Gutter

120

linear feet (5" K-style)

Downspouts Needed

2x3" outlets

Downspout Pipe

linear feet (est.)

Hangers / Brackets

every 2 ft

End Caps

left + right

Miters (Corners)

inside/outside

Drop Outlets

for downspouts

Elbows

downspout elbows

Sealant Tubes

gutter sealant

Did this help?

How to Use This Calculator

Enter your total roof drainage area in square feet (the footprint area that drains to the gutters). Input the rainfall intensity for your area in inches per hour. Select a gutter size, then enter the total gutter run length, number of corners, and roof edges. The calculator sizes the system and lists all components needed.

Formula Used

Adjusted Drainage Area = Roof Area x Rainfall Intensity. Downspouts = Adjusted Area / Downspout Capacity. Hangers = Gutter Length / 2 ft spacing + 1. End Caps = Roof Edges x 2.

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Disclaimer

This calculator is for estimation purposes only. Results may vary based on local conditions, materials, and building codes. Always consult a licensed professional before making decisions based on these calculations. MyContractorTools is not responsible for any errors or omissions.