Culvert Pipe Size Method

Table E: Culvert Pipe Size Required for Drainage Area*

X-Section
Area (Sq. Ft.)

Diameter
(In.)

X-Section
Area (Sq. Ft.)

Diameter
(In.)

0.55	10	12.60	48
0.79	12	15.90	54
1.25	15	19.60	60
1.80	18	23.80	66
3.10	24	28.30	72
4.90	30	33.20	78
7.10	36	38.50	84
9.60	42	44.20	90

*King’s Handbook on Hydraulics, modified by Forestry BMP Handbook Technical Advisory Committee (Courtesy of Rayonier).

Note: For watersheds that require more than 44.2 square feet of pipe (a 90-inch pipe), multiple pipe combinations should be used to meet the requirements. It is generally preferable to use multiple pipes of the same size and the pipes should be spaced leaving a distance of 1/2 the pipe diameter between the pipes. For example, if two 72-inch pipes are required, the pipes should be spaced 36 inches apart.