Calculate volumetric flow rate based on pipe diameter and fluid velocity.
Millimeters (mm)
Centimeters (cm)
Inches (in)
Meters per second (m/s)
Feet per second (ft/s)
Flow Rate (Cubic Meters/Hour):–
Flow Rate (Liters/Minute):–
Flow Rate (US Gallons/Minute):–
Cross-Sectional Area:–
How to Calculate Flow Rate Through a Pipe
Calculating the flow rate of a liquid or gas through a pipe is a fundamental requirement in hydraulic engineering, irrigation planning, and industrial process design. The volumetric flow rate is essentially the volume of fluid that passes through a given cross-section of the pipe per unit of time.
The Continuity Equation Formula
The primary formula used to determine flow rate (Q) when the velocity and pipe dimensions are known is:
Q = A × v
Where:
Q is the volumetric flow rate.
A is the cross-sectional area of the pipe.
v is the average velocity of the fluid.
Step-by-Step Calculation Guide
To calculate the flow rate manually, follow these steps:
Determine the Internal Radius (r): Measure the internal diameter of the pipe and divide it by 2. Ensure you convert this to meters for standard metric calculations.
Calculate the Area (A): Use the formula for the area of a circle: Area = π × r².
Measure Velocity (v): Determine how fast the fluid is moving (usually in meters per second).
Multiply: Multiply the Area by the Velocity to get the flow rate in cubic meters per second (m³/s).
Convert: Multiply by 3,600 to get cubic meters per hour (m³/h) or by 60,000 for liters per minute (LPM).
Example Calculation
Suppose you have a pipe with an internal diameter of 100mm and water traveling at 2 meters per second.
Radius = 0.05 meters (100mm / 2 / 1000)
Area = π × (0.05)² = 0.007854 m²
Flow Rate = 0.007854 m² × 2 m/s = 0.015708 m³/s
In Liters per Minute = 0.015708 × 60,000 = 942.48 LPM
function calculatePipeFlow() {
var diameter = parseFloat(document.getElementById('pipeDiameter').value);
var diameterUnit = document.getElementById('diameterUnit').value;
var velocity = parseFloat(document.getElementById('flowVelocity').value);
var velocityUnit = 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 (diameterUnit === "mm") {
diameterInMeters = diameter / 1000;
} else if (diameterUnit === "cm") {
diameterInMeters = diameter / 100;
} else if (diameterUnit === "in") {
diameterInMeters = diameter * 0.0254;
}
// Convert velocity to m/s
var velocityInMS;
if (velocityUnit === "ms") {
velocityInMS = velocity;
} else if (velocityUnit === "fps") {
velocityInMS = velocity * 0.3048;
}
// Calculate Area (A = pi * r^2)
var radius = diameterInMeters / 2;
var areaM2 = Math.PI * Math.pow(radius, 2);
// Calculate Flow Rate Q (m^3/s)
var flowM3S = areaM2 * velocityInMS;
// Conversions
var flowM3H = flowM3S * 3600;
var flowLPM = flowM3S * 60000;
var flowGPM = flowLPM * 0.264172;
// Display results
document.getElementById('resM3H').innerText = flowM3H.toFixed(3) + " m³/h";
document.getElementById('resLPM').innerText = flowLPM.toFixed(2) + " L/min";
document.getElementById('resGPM').innerText = flowGPM.toFixed(2) + " GPM";
document.getElementById('resArea').innerText = areaM2.toFixed(5) + " m²";
document.getElementById('flowResults').style.display = "block";
}