What orifice flow is
Orifice flow describes fluid discharging through a small opening under a driving head of pressure, such as water draining from a tank through a hole in its side or bottom. It is a common calculation in plumbing, irrigation, hydraulics, and tank-drain design.
The formula
The theoretical jet velocity from Torricelli’s law is v = √(2·g·h), where h is the head (height of fluid above the orifice) and g is gravitational acceleration. The actual flow rate is then Q = Cd × A × v, where A is the orifice’s cross-sectional area and Cd is a discharge coefficient (typically 0.6-0.65 for a sharp-edged circular orifice) that accounts for friction and flow contraction losses.
This calculator is intended for general engineering and educational reference; the exact discharge coefficient for a given orifice should ideally be determined experimentally or taken from manufacturer data for precise applications.