Imperial (Inches / Feet per second)
Metric (mm / Meters per second)
Calculation Results:
Volumetric Flow Rate:0 GPM (Gallons Per Minute)
Volumetric Flow Rate:0 LPM (Liters Per Minute)
Cubic Units:0ft³/h
function toggleUnits() {
var unit = document.getElementById('unitSystem').value;
var labelDiameter = document.getElementById('labelDiameter');
var labelVelocity = document.getElementById('labelVelocity');
if (unit === 'imperial') {
labelDiameter.innerHTML = 'Inner Pipe Diameter (Inches):';
labelVelocity.innerHTML = 'Fluid Velocity (ft/s):';
} else {
labelDiameter.innerHTML = 'Inner Pipe Diameter (mm):';
labelVelocity.innerHTML = 'Fluid Velocity (m/s):';
}
}
function calculateFlowRate() {
var system = document.getElementById('unitSystem').value;
var d = parseFloat(document.getElementById('pipeDiameter').value);
var v = parseFloat(document.getElementById('flowVelocity').value);
var resultDiv = document.getElementById('pumpResult');
if (isNaN(d) || isNaN(v) || d <= 0 || v <= 0) {
alert('Please enter valid positive numbers for diameter and velocity.');
return;
}
var flowGPM, flowLPM, flowCubic, unitCubicText;
var pi = Math.PI;
if (system === 'imperial') {
// Diameter in inches to Area in square feet
var radiusFeet = (d / 12) / 2;
var areaSqFt = pi * Math.pow(radiusFeet, 2);
// Flow in cubic feet per second
var cfs = areaSqFt * v;
flowGPM = cfs * 448.831; // 1 CFS = 448.831 GPM
flowLPM = flowGPM * 3.78541;
flowCubic = cfs * 3600; // Cubic feet per hour
unitCubicText = 'ft³/h';
} else {
// Diameter in mm to Area in square meters
var radiusMeters = (d / 1000) / 2;
var areaSqM = pi * Math.pow(radiusMeters, 2);
// Flow in cubic meters per second
var cms = areaSqM * v;
flowLPM = cms * 60000; // 1 CMS = 60,000 LPM
flowGPM = flowLPM / 3.78541;
flowCubic = cms * 3600; // Cubic meters per hour
unitCubicText = 'm³/h';
}
document.getElementById('flowRateGPM').innerHTML = flowGPM.toFixed(2);
document.getElementById('flowRateLPM').innerHTML = flowLPM.toFixed(2);
document.getElementById('flowRateCubic').innerHTML = flowCubic.toFixed(2);
document.getElementById('unitCubic').innerHTML = unitCubicText;
resultDiv.style.display = 'block';
}
Understanding the Pump Flow Rate Calculation Formula
Calculating the flow rate of a pump is a fundamental task in hydraulic engineering, plumbing, and industrial process design. The flow rate determines how much fluid moves through a system within a specific timeframe, which is critical for sizing pumps, pipes, and control valves.
The Continuity Equation
The most common method for calculating pump flow rate based on pipe dimensions is the Continuity Equation. The formula is expressed as:
Q = A × v
Where:
Q is the Volumetric Flow Rate.
A is the Cross-sectional Area of the pipe.
v is the Flow Velocity of the fluid.
How to Calculate Pipe Area
Since pipes are cylindrical, the cross-sectional area (A) is calculated using the diameter (d) of the inner pipe wall:
A = π × (d / 2)²
It is vital to use the inner diameter (ID), as the outer diameter includes the thickness of the pipe wall, which does not contain the moving fluid.
Step-by-Step Calculation Example
Suppose you have a pump moving water through a pipe with an inner diameter of 4 inches at a velocity of 8 feet per second (ft/s). To find the GPM (Gallons Per Minute):
Calculate Flow in CFS: 0.0872 sq ft × 8 ft/s = 0.6976 Cubic Feet per Second (CFS).
Convert to GPM: 0.6976 × 448.83 ≈ 313.1 GPM.
Why Flow Velocity Matters
In most pumping systems, there are "optimal" velocity ranges. For suction lines, velocity is typically kept between 2 to 4 ft/s to prevent cavitation. For discharge lines, 5 to 10 ft/s is common. If the velocity is too high, you face excessive friction loss and potential pipe damage; if it is too low, solids may settle in the pipe.