Torricelli's theorem states that the velocity of efflux for a nonviscous fluid flowing from a cylindrical tank is

where

is the acceleration due to gravity (10

) and

is the distance between the surface of the water and the location of the spigot. However, this does not specify the exact coefficient because it assumes that the velocity of the water at the surface of the tank is negligible and that both the tank and the spigot are exposed to atmospheric pressure. If the velocity of the water at the surface is taken into account, the formula for the velocity of efflux becomes

, where it takes into account

r, the radius of the spigot, and

R, the radius of the cylindrical tank. This equation can be derived from Bernoulli's equation,

, and the continuity equation,

.