Calculate Rain Gutter Size

Then use the chart below to see what size gutter you need.

Calculate rain gutter size.

Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage. Find the width of the gutters. The total rainfall and how rapidly it falls will affect the runoff from the roof. Multiply the drainage area by the roof pitch factor and rainfall intensity to find out the adjusted square footage.

The downspout and gutter sizing calculator is located on the tools cad and apps page of the smacna website. For example a 5 inch gutter system requires at least 2 x 3 downspouts and a 6 inch gutter system requires 3 x 4 downspouts. 5 inch 5 520 square feet. 6 inch 7 960 square feet.

To limit the effects of thermal expansion in gutters 50 ft. Gather some basic weather information to calculate the proper size for gutters and downspouts for a house. Downspout sizes must not exceed the bottom width of the gutter. Match your downspouts to the gutter size you chose in step 7.

The gutter and downspout size required is highly dependent on the amount of gutter and the spacing of the downspouts. 5 inch 5 520 square feet. Gutters typically come in 5 or 6 in 13 or 15 cm sizes and can be k style or half round place a sturdy 20 ft 6 1 m ladder on 1 side of your house so that you can reach the gutters. Please lower the maximum spacing between downspouts to see this effect.

Simplified suitable for flattish roofs with little or no vertical faces or steep roofs draining to one side of box gutter only or any roof if you are in a hurry and make the necessary allowances for all catchments. If a roof s various drainage areas call for different size gutters go for the biggest one k style. An inch of rain is not much but it if falls in half an hour it could flood a gutter. Determine the size of your downspout.

Adding additional downspouts will require less gutter and downspout volume resulting in smaller gutters downspouts. Total roof area also affects runoff. Refer to the gutter packaging or specification for the recommended downspout size. If a roof s various drainage areas call for different size gutters go for the biggest one k style.

Now architects engineers designers and contractors can easily and accurately size downspouts and gutters according to the specifications in smacna s architectural sheet metal manual 7th edition 2012. Box gutter with rain water head at end of box gutter. There is no limit to downpipe size or eaves gutter size. Calculations are based on level gutter capacity as experimentally determined by the national institute of standards and technology nist.