Enter your Pipe Diameter and Flow Velocity (or Volume and Time) into the Flow Rate Calculator to find your Flow Rate in any unit — plus automatic conversions to GPM and L/s, and the pipe's Cross-Sectional Area.
Flow Rate
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Flow Rate (GPM)
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Flow Rate (L/s)
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Cross-Sectional Area
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Flow rate is the volume of fluid that passes through a given cross-sectional area per unit time. It's commonly expressed in units like gallons per minute (GPM), cubic feet per second, or liters per second.
Flow rate equals the cross-sectional area of the pipe times the velocity of the fluid. The formula is Q = A × V, where A = π × (diameter/2)² and V is the velocity.
To convert volumetric flow rate to mass flow rate, multiply the volumetric flow rate by the fluid's density. Mass flow rate = Volumetric flow rate × Density.
Maximum flow rate is the highest volume of fluid that can pass through a pipe or system under given conditions. It's limited by factors like pipe diameter, pressure, and fluid properties.
To find velocity from flow rate, divide the flow rate by the cross-sectional area of the pipe: Velocity = Flow Rate ÷ Area, where Area = π × (diameter/2)².
Common flow rate units include gallons per minute (GPM), cubic feet per second (CFS), liters per second (L/s), and cubic meters per hour (m³/h). Our calculator supports conversions between multiple unit systems.
Flow rate increases with the square of the pipe diameter. Doubling the diameter increases the cross-sectional area by four times, which can significantly increase flow rate if velocity remains constant.