PSI to GPM Calculator

Pressure and flow describe different properties of a fluid system, so PSI cannot be converted to GPM with a universal unit factor. Pressure is force per area, while gallons per minute measures volume moving over time. A useful estimate requires information about the restriction through which the liquid flows. For valves, regulators, and similar fittings, that information is commonly represented by the flow coefficient Cv. This calculator applies the established liquid-flow relationship: flow equals Cv multiplied by the square root of pressure difference divided by specific gravity. Pressure difference means the upstream pressure minus the downstream pressure, not necessarily the system gauge pressure shown on one instrument. If a valve has 70 PSI upstream and 45 PSI downstream, enter 25 PSI. Cv is supplied by the valve or component manufacturer and represents the number of US gallons of water per minute that passes through the component at a one PSI pressure drop under defined conditions. A larger Cv generally means less restriction and more flow at the same pressure drop. Specific gravity adjusts the water-based Cv rating for another liquid. Water near standard reference conditions has a specific gravity of approximately 1. A liquid with a specific gravity of 1.44 is denser than water and produces less flow through the same valve under the same pressure difference. Light liquids with values below 1 produce a higher calculated flow. Use a property value appropriate to the liquid temperature because density can change with temperature. The equation is intended for steady, incompressible liquid flow without flashing or cavitation. It is not a complete pipe-network model and should not be used for gases or steam. Actual flow can also be affected by pipe length, fittings, roughness, viscosity, elevation, pump curves, partially open valves, and measurement uncertainty. Manufacturer sizing methods may include correction factors for unusually viscous fluids, attached fittings, or choked-flow conditions. Use the result for preliminary valve sizing, irrigation checks, water-system comparisons, and engineering estimates. For safety-critical design, verify the selected Cv, pressure conditions, units, and fluid properties against current manufacturer data and applicable standards. A measured flow test remains the best confirmation of real installed performance.