Power in kilowatts can be determined by the following equation:

**kW = H x Q x 62.4 x 0.746 ÷ 550 x e**

where

H = head, in ft.

Q = flow, in cubic ft. per second

62.4 lbs. = weight of 1 cubic ft. of water

0.746 kW = 1 hp

550 foot-lbs./sec. = 1 hp

e = an overall efficiency factor* (usually 0.5 for small microhydro systems)

Combining and reducing all these factors results in the following equation:

**kW = H x Q ÷ 24, when using cfs; or**

**W = H x Q ÷ 12, when using gpm**

*Note that the efficiency factor can range from 9 for larger AC systems to 13 or more for smaller battery-based systems, and will need to be estimated for your specific site.