Method: Orifice area = π × diameter² ÷ 4. Theoretical exit velocity = √(2gh). Actual discharge is estimated using: Q = C_d × A × √(2gh) where Q is flow rate, C_d is the discharge coefficient, A is orifice area, g is gravitational acceleration and h is water head above the orifice. A discharge coefficient near 0.61 is commonly used for a fully contracted sharp-edged orifice, but the actual coefficient varies with orifice geometry, edge condition, approach flow and surrounding boundaries. This calculator assumes free discharge to a lower-pressure region and does not account for submerged downstream conditions or significant approach velocity.