Flow Rate Calculator
Calculates volumetric flow rate through pipes and ducts from cross-section area and velocity
Inner diameter of the pipe in inches
Speed of fluid through the pipe in feet per second
Enter pipe diameter and velocity to calculate flow rate
Flow rate in gallons per minute
Flow rate in liters per minute
Frequently Asked Questions
What is flow rate?
Flow rate is the volume of fluid passing through a pipe or duct per unit of time. It is calculated by multiplying the cross-sectional area of the pipe by the velocity of the fluid. Common units are gallons per minute (GPM), cubic feet per second (CFS), and liters per minute (LPM).
How does pipe diameter affect flow rate?
Flow rate is proportional to the square of the diameter. Doubling the pipe diameter quadruples the cross-sectional area and thus the flow rate at the same velocity. This is why even small increases in pipe size can significantly increase capacity.
What is a typical water velocity in pipes?
Residential water pipes typically have velocities between 2 and 8 feet per second. Velocities above 8 fps can cause noise, erosion, and water hammer. The ideal range for most plumbing is 4-6 fps, balancing adequate flow with minimal turbulence.
How do I convert GPM to liters per minute?
Multiply gallons per minute by 3.78541 to get liters per minute. One GPM equals about 3.785 LPM. Going the other direction, divide liters per minute by 3.785 to get GPM. This conversion is needed when working with metric and imperial plumbing specifications.
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