Meters per second (m/s)
Feet per second (ft/s)
Kilometers per hour (km/h)
Calculation Results
Cubic Meters per Hour
Liters per Minute (LPM)
US Gallons per Minute (GPM)
Cubic Feet per Second (CFS)
Understanding Volumetric Flow Rate
Volumetric flow rate is the volume of fluid which passes per unit time through a specific cross-sectional area, such as a pipe or duct. In fluid dynamics, this is a fundamental calculation used by mechanical engineers, civil engineers, and hydrologists to design piping systems, irrigation networks, and HVAC systems.
The Flow Rate Formula
The calculation is based on the principle that the flow rate (Q) is equal to the cross-sectional area (A) of the pipe multiplied by the average velocity (v) of the fluid:
Q = A × v
Where:
Q: Volumetric Flow Rate
A: Cross-sectional area of the pipe (π × r²)
v: Flow Velocity
Practical Example
Imagine you have a pipe with an internal diameter of 100 mm and water moving through it at a velocity of 1.5 meters per second.
First, calculate the area in meters: Radius = 0.05m. Area = π × (0.05)² = 0.007854 m².
Calculate flow: Q = 0.007854 m² × 1.5 m/s = 0.011781 m³/s.
Convert to hourly: 0.011781 × 3600 = 42.41 m³/h.
Key Factors Influencing Flow
While the formula provides a theoretical value, real-world applications must account for:
Pipe Friction: Roughness inside the pipe slows down the fluid.
Viscosity: Thicker fluids (like oil) flow differently than water.
Pressure: Differential pressure is often what drives the velocity in the first place.
Flow Regime: Whether the flow is Laminar (smooth) or Turbulent (chaotic) affects the velocity profile.
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
var diameterInMeters;
if (dUnit === "mm") {
diameterInMeters = diameter / 1000;
} else if (dUnit === "cm") {
diameterInMeters = diameter / 100;
} else if (dUnit === "in") {
diameterInMeters = diameter * 0.0254;
} else {
diameterInMeters = diameter;
}
// Convert Velocity to Meters per Second
var velocityInMS;
if (vUnit === "fs") {
velocityInMS = velocity * 0.3048;
} else if (vUnit === "kmh") {
velocityInMS = velocity / 3.6;
} else {
velocityInMS = velocity;
}
// Calculate Area (A = pi * r^2)
var radius = diameterInMeters / 2;
var area = Math.PI * Math.pow(radius, 2);
// Calculate Flow Rate in m3/s
var flowM3S = area * velocityInMS;
// Convert to various units
var flowM3H = flowM3S * 3600;
var flowLPM = flowM3S * 60000;
var flowGPM = flowM3S * 15850.3231;
var flowCFS = flowM3S * 35.3147;
// Display Results
document.getElementById("resM3H").innerText = flowM3H.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 4}) + " m³/h";
document.getElementById("resLPM").innerText = flowLPM.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " LPM";
document.getElementById("resGPM").innerText = flowGPM.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " GPM";
document.getElementById("resCFS").innerText = flowCFS.toLocaleString(undefined, {minimumFractionDigits: 4, maximumFractionDigits: 6}) + " ft³/s";
document.getElementById("flowResult").style.display = "block";
}