Calculate the volumetric flow rate based on pipe diameter and fluid velocity.
Metric (mm / m/s)
Imperial (inches / ft/s)
Calculated Results
How to Calculate Flow Rate from Pipe Diameter
Calculating the flow rate (Q) of a fluid moving through a pipe is a fundamental concept in hydraulics and fluid dynamics. To determine this value, you need two primary measurements: the internal cross-sectional area of the pipe and the average velocity of the fluid moving through it.
Q = A × v
Where:
Q is the volumetric flow rate.
A is the cross-sectional area of the pipe (π × r²).
v is the fluid velocity.
Step-by-Step Calculation Guide
Follow these steps to perform the calculation manually:
Measure the Diameter: Find the internal diameter (D) of the pipe. If you have the outer diameter, subtract the wall thickness twice.
Calculate the Radius: Divide the diameter by 2 (r = D/2).
Find the Area: Use the formula A = π × r². Ensure your units are consistent (e.g., convert millimeters to meters).
Determine Velocity: Measure or estimate the fluid velocity (v) in meters per second or feet per second.
Multiply: Multiply the Area by the Velocity to get the flow rate in cubic units per second.
Example Calculation (Metric)
Imagine you have a pipe with an internal diameter of 100 mm and water traveling at 2 meters per second.
Convert Diameter to meters: 100mm = 0.1m.
Radius: 0.05m.
Area: π × (0.05)² = 0.007854 m².
Flow Rate: 0.007854 m² × 2 m/s = 0.0157 m³/s.
In Liters: 0.0157 × 1000 = 15.7 Liters per second.
function updateUnits() {
var system = document.getElementById('calcSystem').value;
var labelD = document.getElementById('labelDiameter');
var labelV = document.getElementById('labelVelocity');
if (system === 'metric') {
labelD.innerText = 'Internal Pipe Diameter (mm)';
labelV.innerText = 'Fluid Velocity (m/s)';
} else {
labelD.innerText = 'Internal Pipe Diameter (inches)';
labelV.innerText = 'Fluid Velocity (ft/s)';
}
}
function calculateFlow() {
var diameter = parseFloat(document.getElementById('pipeDiameter').value);
var velocity = parseFloat(document.getElementById('flowVelocity').value);
var system = document.getElementById('calcSystem').value;
var resultBox = document.getElementById('resultBox');
var resultOutput = document.getElementById('resultOutput');
if (isNaN(diameter) || isNaN(velocity) || diameter <= 0 || velocity < 0) {
alert('Please enter valid positive numbers for diameter and velocity.');
return;
}
var area, flowRate, displayHtml;
var pi = Math.PI;
if (system === 'metric') {
// Convert mm to meters
var dMeters = diameter / 1000;
var radius = dMeters / 2;
area = pi * Math.pow(radius, 2); // m2
flowRate = area * velocity; // m3/s
var litersPerSec = flowRate * 1000;
var litersPerMin = litersPerSec * 60;
var cubicMetersPerHour = flowRate * 3600;
displayHtml = 'Flow Rate (m³/s): ' + flowRate.toFixed(4) + '';
displayHtml += 'Flow Rate (Liters/sec): ' + litersPerSec.toFixed(2) + '';
displayHtml += 'Flow Rate (Liters/min): ' + litersPerMin.toFixed(2) + '';
displayHtml += 'Flow Rate (m³/hr): ' + cubicMetersPerHour.toFixed(2) + '';
} else {
// Imperial: Diameter in inches, velocity in ft/s
var dFeet = diameter / 12;
var radiusF = dFeet / 2;
area = pi * Math.pow(radiusF, 2); // ft2
flowRate = area * velocity; // ft3/s
var gpm = flowRate * 448.831; // 1 ft3/s = 448.831 GPM
var cubicFeetPerMin = flowRate * 60;
displayHtml = 'Flow Rate (ft³/s): ' + flowRate.toFixed(4) + '';
displayHtml += 'Flow Rate (Gallons/min – GPM): ' + gpm.toFixed(2) + '';
displayHtml += 'Flow Rate (ft³/min): ' + cubicFeetPerMin.toFixed(2) + '';
}
resultOutput.innerHTML = displayHtml;
resultBox.style.display = 'block';
}