Orifice Flow Calculator

An orifice restricts a fluid stream by forcing it through an opening smaller than the surrounding pipe or vessel. The pressure difference across that restriction converts pressure energy into kinetic energy, creating a fast jet. This calculator applies the standard incompressible orifice equation: volume flow equals the discharge coefficient multiplied by opening area and by the square root of twice the pressure difference divided by fluid density. For a circular opening, area is pi multiplied by diameter squared and divided by four. The discharge coefficient corrects the ideal Bernoulli result for contraction and energy loss. A sharp-edged thin plate commonly has a coefficient near 0.60 to 0.65, while a smoothly rounded nozzle can have a value closer to one. The correct coefficient depends on opening geometry, plate thickness, Reynolds number, installation, and tap locations. The ideal jet velocity shown separately does not include the coefficient; actual average discharge velocity can be represented by multiplying it by the coefficient. Enter diameter in millimetres, pressure difference in pascals, density in kilograms per cubic metre, and a dimensionless discharge coefficient. The calculator converts diameter to metres before computing area and reports flow in both cubic metres per second and litres per second. Pressure difference must be the upstream static pressure minus downstream static pressure. Density should represent the fluid at operating temperature and pressure. Water near room temperature is about 998 kilograms per cubic metre, while gases are much less dense and can accelerate strongly for the same pressure difference. This simple equation is best for steady, incompressible flow with a known coefficient. Large gas pressure drops require compressible-flow methods because density changes through the restriction and sonic choking may occur. Cavitation can also invalidate a liquid calculation if local pressure falls below vapor pressure. Pipe diameter and beta ratio matter when an orifice plate is used as a calibrated flow meter, and professional metering standards add expansion, velocity-of-approach, and Reynolds corrections. Use this result for preliminary sizing, laboratory checks, irrigation outlets, tank drains under known pressure, and approximate hydraulic calculations. Confirm critical designs against an applicable standard or manufacturer data. Accurate measurements require calibrated pressure sensors, correct tap placement, stable flow, and a discharge coefficient suited to the real geometry rather than a generic estimate.