Submittal Builder

Submittal Builder

Gutter Calculator

This application uses the equations that are laid out in the SMACNA handbook. It should be used to calculate required gutter size, downspout size, and downspout spacing for your roof perimeter. Please Note: This calculator should serve as an information source only. Metal-Era, Inc. assumes no responsibility for problems which may arise from using this calculator and recommends that you verify all data obtained. For further assistance, please email us at or call 800-558-2162.


Select the State/City nearest you:
Plan Width (ft):
Plan Length (ft):
Slope (in/ft): (decimal)
Total Gutter Length (ft):
Max Gutter Per Downspout (ft):
Storm Requirement:
Ratio of Depth to Width of Gutter:
[GT-1 Calc] Zip Code
[GT-1 Calc] Roof Height
[GT-1 Calc] Building Category
[GT-1 Calc] Building Exposure

Project Name:
Print Results

 Drainage Results

 Rainfall Intensity (10yr) = 6.6 in/hr
 Rainfall Intensity (100yr) = 9.1 in/hr
 Drainable Area (10yr) = 180 sq. ft
 Drainable Area (100yr) = 130 sq. ft
 Plan Area =
 Design Area =
 Min Number of Downspouts =
 Max Area Served by Each DS =

 Minimum Gutter Width =
 Minimum Gutter Depth =
 Minimum Downspout Size =

GT-1 Results
 Horizontal Perimeter Pressure =
 Vertical Perimeter Pressure =
 Horizontal Corner Pressure =
 Vertical Corner Pressure =

Metal-Era Gutter Products

Click Here for more information about Metal-Era advanced drainage systems

Plan Width: The width of the rectangular roof area in feet. You may round up to the nearest foot.
Plan Length: The length (alternate dimension) of the roof in feet, again rounded up.
Slope: The slope of the roof in inches per foot (decimal for fraction of an inch).
Total Gutter Length: The length of all gutter serving this roof in feet (rounded up).
Maximum Gutter Per DS: The maximum length of gutter served by one downspout in feet (rounded).
Storm Requirement: Selects the rainfall intensity lasting 5 minutes for storms occurring in your area. Also selects The amount of roof area that can be drained by one square inch of downspout. These can be set based on storms occuring every 10 or 100 years.
Ratio of Depth to Width of Gutter: The relation of depth to width. (e.g. depth = .75 * width)