The discharge through a large rectangular orifice is given by (where H1 = Height of the liquid above the top of the orifice, H2 = Height of the liquid above the bottom of the orifice, b = Breadth of the orifice, and Cd = Coefficient of discharge)

• Q = Cd x b2g(H2 - H1)
• Q = Cd x b2g(H21/2 - H11/2)
• Q = Cd x b2g(H23/2 - H13/2)
• Q = Cd x b2g(H22 - H12)