Calculate the volumetric flow rate based on pipe diameter and water velocity.
Inches
mm
cm
m/s
ft/s
Liters per Minute: 0 L/min
US Gallons per Minute: 0 GPM
Cubic Meters per Hour: 0 m³/h
Cubic Feet per Second: 0 ft³/s
How to Calculate Flow Rate in a Pipe
Understanding how much water is moving through a pipe is essential for plumbing, irrigation, and industrial engineering. The volumetric flow rate (Q) is determined by the cross-sectional area of the pipe (A) and the velocity of the fluid (v).
The fundamental formula for flow rate is:
Q = A × v
Where:
Q is the volumetric flow rate.
A is the cross-sectional area ($\pi \times r^2$).
v is the flow velocity.
Step-by-Step Calculation Guide
To calculate the flow rate manually, follow these steps:
Determine the Internal Diameter: Measure the inside diameter (d) of the pipe. If you have the radius (r), remember that $d = 2r$.
Calculate the Area: Use the formula $Area = \pi \times (diameter / 2)^2$. Ensure your units are consistent (e.g., meters).
Measure Velocity: Determine how fast the water is moving, usually in meters per second (m/s) or feet per second (ft/s).
Multiply: Multiply the area by the velocity to get the flow rate in cubic units per second.
Practical Example:
Suppose you have a pipe with an internal diameter of 2 inches and water moving at 5 feet per second.
Convert diameter to feet: 2 inches = 0.1667 feet.
Calculate Area: $\pi \times (0.0833)^2 = 0.0218$ sq. ft.
Calculate Flow: $0.0218 \times 5 = 0.109$ cubic feet per second (CFS).
Convert to GPM: $0.109 \times 448.83 = \mathbf{48.92}$ GPM.
Common Water Velocity Recommendations
In most domestic plumbing systems, water velocity is kept within specific ranges to prevent noise, pipe erosion, and water hammer:
Service Lines: 4 to 8 feet per second (1.2 to 2.4 m/s).
Internal Plumbing: 3 to 5 feet per second (0.9 to 1.5 m/s).
Suction Lines: 2 to 4 feet per second (0.6 to 1.2 m/s).
function calculateFlow() {
var d = parseFloat(document.getElementById("pipeDiameter").value);
var dUnit = document.getElementById("diameterUnit").value;
var v = parseFloat(document.getElementById("velocity").value);
var vUnit = document.getElementById("velocityUnit").value;
if (isNaN(d) || d <= 0 || isNaN(v) || v <= 0) {
alert("Please enter valid positive numbers for diameter and velocity.");
return;
}
var dMeters;
if (dUnit === "inches") {
dMeters = d * 0.0254;
} else if (dUnit === "mm") {
dMeters = d / 1000;
} else {
dMeters = d / 100;
}
var vMps;
if (vUnit === "fps") {
vMps = v * 0.3048;
} else {
vMps = v;
}
var radius = dMeters / 2;
var area = Math.PI * Math.pow(radius, 2);
var qM3s = area * vMps;
var lpm = qM3s * 60000;
var gpm = qM3s * 15850.3231;
var m3h = qM3s * 3600;
var cfs = qM3s * 35.3147;
document.getElementById("resLpm").innerText = lpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resGpm").innerText = gpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resM3h").innerText = m3h.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
document.getElementById("resCfs").innerText = cfs.toLocaleString(undefined, {minimumFractionDigits: 4, maximumFractionDigits: 4});
document.getElementById("flowResult").style.display = "block";
}