Calculate volumetric flow rate based on pipe diameter and fluid velocity.
Inches
mm
cm
ft/s
m/s
US Gallons Per Minute (GPM):
Liters Per Minute (L/min):
Cubic Feet per Second (CFS):
Cubic Meters per Hour (m³/h):
How to Calculate Total Flow Rate
Flow rate is the volume of fluid which passes per unit time. In fluid dynamics, this is usually measured through a pipe or a channel. To calculate the total flow rate, you need to know the cross-sectional area of the pipe and the velocity at which the fluid is moving.
Q = A × v
Where:
Q is the Volumetric Flow Rate.
A is the Cross-sectional Area of the pipe (π × r²).
v is the Flow Velocity.
Step-by-Step Calculation Guide
Follow these steps to determine your flow rate manually:
Find the Internal Diameter: Measure the inside width of your pipe. For example, a "2-inch pipe" often has a specific internal diameter depending on its schedule (thickness).
Calculate Area: Convert the diameter to a radius (diameter / 2). Use the formula A = πr². If your radius is in inches, your area will be in square inches.
Measure Velocity: Determine how fast the fluid is moving (feet per second or meters per second).
Multiply and Convert: Multiply Area by Velocity. Ensure your units match (e.g., convert square inches to square feet if velocity is in feet per second).
Practical Example
Imagine a pipe with an internal diameter of 4 inches and a fluid velocity of 8 feet per second:
Radius = 2 inches = 0.1667 feet.
Area = π × (0.1667)² ≈ 0.0872 square feet.
Flow Rate (Q) = 0.0872 sq ft × 8 ft/s = 0.6976 Cubic Feet per Second (CFS).
To get GPM: 0.6976 × 448.83 ≈ 313.1 GPM.
Common Flow Rate Units
Different industries use different metrics:
GPM: Used in US residential and commercial plumbing/irrigation.
L/min: Standard metric unit for small to medium flows.
m³/h: Used in industrial water treatment and large scale pumping.
CFS: Common in hydrology and environmental river flow monitoring.
function calculateFlowRate() {
var diameter = parseFloat(document.getElementById("pipeDiameter").value);
var dUnit = document.getElementById("diameterUnit").value;
var velocity = parseFloat(document.getElementById("flowVelocity").value);
var vUnit = document.getElementById("velocityUnit").value;
if (isNaN(diameter) || isNaN(velocity) || diameter <= 0 || velocity <= 0) {
alert("Please enter valid positive numbers for diameter and velocity.");
return;
}
// Convert diameter to meters for standard calculation
var dMeters;
if (dUnit === "in") {
dMeters = diameter * 0.0254;
} else if (dUnit === "mm") {
dMeters = diameter / 1000;
} else if (dUnit === "cm") {
dMeters = diameter / 100;
}
// Convert velocity to meters per second
var vMPS;
if (vUnit === "fps") {
vMPS = velocity * 0.3048;
} else {
vMPS = velocity;
}
// Calculate Area in square meters (A = pi * r^2)
var radius = dMeters / 2;
var area = Math.PI * Math.pow(radius, 2);
// Flow Rate in Cubic Meters per Second (m3/s)
var qCMS = area * vMPS;
// Convert to various units
var lps = qCMS * 1000;
var lpm = lps * 60;
var gpm = qCMS * 15850.323141; // 1 m3/s = 15850.32 GPM
var cfs = qCMS * 35.3147;
var cmh = qCMS * 3600;
// Display results
document.getElementById("resGPM").innerText = gpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resLPM").innerText = lpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resCFS").innerText = cfs.toLocaleString(undefined, {minimumFractionDigits: 4, maximumFractionDigits: 4});
document.getElementById("resCMH").innerText = cmh.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("flowResult").style.display = "block";
}