Please enter valid positive numbers for diameter and velocity.
Flow Rate (US GPM):–
Flow Rate (m³/hr):–
Flow Rate (Liters/min):–
Pipe Cross-Section Area:–
function calculateFlowRate() {
// Get Inputs
var diameterInput = document.getElementById('pipeDiameter').value;
var diaUnit = document.getElementById('diaUnit').value;
var velocityInput = document.getElementById('flowVelocity').value;
var velUnit = document.getElementById('velUnit').value;
var errorMsg = document.getElementById('errorMsg');
var resultsBox = document.getElementById('results');
// Validation
if (diameterInput === "" || velocityInput === "" || isNaN(diameterInput) || isNaN(velocityInput)) {
errorMsg.style.display = "block";
errorMsg.innerHTML = "Please enter valid numeric values.";
resultsBox.style.display = "none";
return;
}
var d = parseFloat(diameterInput);
var v = parseFloat(velocityInput);
if (d <= 0 || v < 0) {
errorMsg.style.display = "block";
errorMsg.innerHTML = "Diameter must be positive and velocity non-negative.";
resultsBox.style.display = "none";
return;
}
errorMsg.style.display = "none";
// Normalize Inputs to SI Units (Meters and Meters/Second)
var diameterMeters = 0;
if (diaUnit === 'inch') {
diameterMeters = d * 0.0254;
} else if (diaUnit === 'mm') {
diameterMeters = d / 1000;
} else if (diaUnit === 'ft') {
diameterMeters = d * 0.3048;
} else {
diameterMeters = d; // already meters
}
var velocityMS = 0;
if (velUnit === 'fts') {
velocityMS = v * 0.3048;
} else {
velocityMS = v; // already m/s
}
// Calculation: Area = PI * (D/2)^2
var radius = diameterMeters / 2;
var areaM2 = Math.PI * Math.pow(radius, 2);
// Calculation: Flow Rate (Q) = Area * Velocity (Result in m³/s)
var flowM3S = areaM2 * velocityMS;
// Conversions for Output
// 1 m³/s = 15,850.3231 US Gallons per Minute
var gpm = flowM3S * 15850.3231;
// 1 m³/s = 3600 m³/hr
var m3h = flowM3S * 3600;
// 1 m³/s = 60,000 Liters per Minute
var lpm = flowM3S * 60000;
// Area display (cm² for readability usually, but lets do m²)
var areaDisplay = areaM2.toFixed(4) + " m²";
if (areaM2 < 0.01) {
// Show cm² if very small
areaDisplay = (areaM2 * 10000).toFixed(2) + " cm²";
}
// Display Results
document.getElementById('resGPM').innerHTML = gpm.toFixed(2) + " GPM";
document.getElementById('resM3H').innerHTML = m3h.toFixed(2) + " m³/hr";
document.getElementById('resLPM').innerHTML = lpm.toFixed(2) + " L/min";
document.getElementById('resArea').innerHTML = areaDisplay;
resultsBox.style.display = "block";
}
How to Calculate Piping Flow Rate
Understanding the volumetric flow rate of a fluid through a piping system is fundamental for engineers, plumbers, and technicians. Whether you are designing an HVAC system, sizing an irrigation pump, or managing industrial process fluids, knowing how much fluid passes through a pipe per unit of time is critical. This Piping Flow Rate Calculator allows you to quickly determine the flow rate based on the pipe's internal diameter and the fluid's velocity.
The Physics of Flow Rate
The calculation of liquid flow through a pipe relies on the continuity equation for incompressible fluids. The relationship is linear: the volumetric flow rate is equal to the cross-sectional area of the pipe multiplied by the average velocity of the fluid.
Formula: Q = A × v
Where:
Q = Volumetric Flow Rate (e.g., m³/s, GPM)
A = Cross-Sectional Area of the pipe (e.g., m², ft²)
v = Average Fluid Velocity (e.g., m/s, ft/s)
Calculating the Cross-Sectional Area (A)
Most pipes are cylindrical. To find the area, you must first know the Inner Diameter (ID) of the pipe. It is crucial to use the ID rather than the Nominal Pipe Size (NPS) or Outer Diameter (OD), as the wall thickness of the pipe does not carry fluid.
Area (A) = π × (D / 2)²
OR
Area (A) = (π × D²) / 4
Practical Example Calculation
Let's calculate the flow rate for a common scenario found in water supply systems.
Scenario: You have a pipe with an internal diameter of 4 inches. The water is moving at a velocity of 5 feet per second (ft/s). What is the flow rate in Gallons Per Minute (GPM)?
When designing piping systems, velocity is a balancing act. If the velocity is too low, solids suspended in the fluid may settle, leading to clogging (sedimentation). If the velocity is too high, it causes excessive friction loss (pressure drop), noise, and potential pipe erosion.
Typical Water Velocities: 3 to 10 ft/s (approx. 1 to 3 m/s) depending on the application.
Suction Lines: Usually require lower velocities to prevent cavitation in pumps.
Discharge Lines: Can tolerate higher velocities.
Common Units Conversion
Flow rate calculations often involve mixing metric and imperial units. Here are common conversions this calculator handles automatically:
1 Gallon per Minute (US GPM) ≈ 3.785 Liters per Minute
1 Cubic Meter per Hour (m³/hr) ≈ 4.403 GPM
1 Inch = 25.4 Millimeters
Use the tool above to eliminate manual conversion errors and get accurate flow estimates instantly.