Calculate liquid flow based on pipe diameter and velocity
Inches (in)
Millimeters (mm)
Centimeters (cm)
Feet per second (ft/s)
Meters per second (m/s)
Gallons Per Minute (GPM):0
Liters Per Minute (L/min):0
Cubic Meters Per Hour (m³/h):0
How to Calculate Pump Flow Rate
Flow rate is the volume of fluid which passes per unit of time. In pumping systems, understanding the flow rate is critical for sizing pumps, pipes, and control valves. The most common way to calculate flow rate in a pressurized pipe is using the cross-sectional area and the velocity of the fluid.
The Mathematical Formula
The basic formula for flow rate (Q) is:
Q = A × v
Q: Flow Rate
A: Cross-sectional Area of the pipe (π × r²)
v: Velocity of the fluid
Why Velocity Matters
In most industrial and domestic water systems, there are recommended velocity ranges to prevent issues:
Application
Recommended Velocity (ft/s)
Recommended Velocity (m/s)
Pump Suction Lines
2 – 4
0.6 – 1.2
Pump Discharge Lines
5 – 10
1.5 – 3.0
General Water Service
4 – 8
1.2 – 2.4
Practical Example
Suppose you have a pipe with an internal diameter of 4 inches and a flow velocity of 6 feet per second:
Convert diameter to radius: 2 inches (0.1667 feet).
While the calculation above gives you the theoretical flow, real-world pump performance depends on:
Total Dynamic Head (TDH): The total equivalent height that the fluid must be pumped, including friction losses.
Fluid Viscosity: Thicker fluids (like oil) require more power and flow differently than water.
Pump Efficiency: No pump is 100% efficient; some energy is lost to heat and vibration.
NPSH: Net Positive Suction Head ensures the pump does not cavitate.
function calculateFlow() {
var d = parseFloat(document.getElementById('pipeDiameter').value);
var v = parseFloat(document.getElementById('velocity').value);
var dUnit = document.getElementById('diameterUnit').value;
var vUnit = document.getElementById('velocityUnit').value;
if (isNaN(d) || isNaN(v) || d <= 0 || v <= 0) {
alert("Please enter valid positive numbers for diameter and velocity.");
return;
}
// Convert Diameter to Meters
var dMeters;
if (dUnit === "in") {
dMeters = d * 0.0254;
} else if (dUnit === "mm") {
dMeters = d / 1000;
} else {
dMeters = d / 100;
}
// Convert Velocity to Meters Per Second
var vMPS;
if (vUnit === "fps") {
vMPS = v * 0.3048;
} else {
vMPS = v;
}
// Calculate Area (m2) = PI * r^2
var radius = dMeters / 2;
var area = Math.PI * Math.pow(radius, 2);
// Flow Rate in Cubic Meters Per Second (m3/s)
var qMPS = area * vMPS;
// Convert to various units
// 1 m3/s = 15850.3231 US GPM
var gpm = qMPS * 15850.3231;
// 1 m3/s = 60000 L/min
var lpm = qMPS * 60000;
// 1 m3/s = 3600 m3/h
var cmh = qMPS * 3600;
// Display Results
document.getElementById('resGPM').innerText = gpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resLPM').innerText = lpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resCMH').innerText = cmh.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById('resultArea').style.display = 'block';
}