Gutter Calculator
Enter your house size to get the gutters you need, plus downspouts and an estimated cost.
Gutters needed
Estimated cost
How to calculate gutters
Gutters run around the roof edge. For a rectangular house, add length and width, double it, and you have the gutter length. Downspouts go about every 40 ft.
Formula: gutter length = 2 × (length + width), and downspouts = gutter length ÷ 40, rounded up
Worked example: 40 ft × 30 ft house
Gutter length = 2 × (40 + 30) = 140 ft. Downspouts: 140 ÷ 40 = 3.5, rounded up to 4 downspouts.
Where do downspouts go?
Place one about every 40 ft, plus one at each roof valley and corner. Water should drain away from the foundation, not towards it.
Common house sizes
Cost tips
Prices on this page are editable estimates, not quotes. Get 2 to 3 local quotes before you buy, and ask if delivery is included. Delivery, tax and waste can change the total a lot. Order a little extra for cuts and breakage, and confirm final quantities with your supplier or a qualified professional.
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Frequently asked questions
How many feet of gutter do I need for a 40x30 house?
A 40 ft by 30 ft house needs 140 ft of gutter and 4 downspouts, at one downspout per 40 ft.
How far apart should downspouts be?
About every 40 ft, and at least one per roof valley and corner.
Do I need gutters on all sides?
Usually yes, but at minimum on sides where water falls near doors, walkways and foundations.
Does this include corners and end caps?
No, this counts gutter length and downspouts only. Corners, end caps and brackets are extra.
Are the prices accurate?
Prices are editable estimates. The defaults are typical US figures, and your local price can be higher or lower. Fitting is not included.