.calculator-container {
max-width: 800px;
margin: 0 auto;
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
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.calc-box {
background: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
margin-bottom: 40px;
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.calc-title {
text-align: center;
color: #2c3e50;
margin-bottom: 25px;
font-size: 24px;
font-weight: 700;
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How to Calculate Flow Rate of Fluid in a Pipe
Understanding how to calculate the volumetric flow rate of a fluid passing through a pipe is fundamental in engineering, plumbing, and irrigation. The flow rate describes the volume of fluid that passes a specific point in a system per unit of time.
The Flow Rate Formula
The most basic equation for calculating volumetric flow rate (Q) relies on knowing the cross-sectional area of the pipe and the average velocity of the fluid moving through it. The formula is:
Q = A × v
Where:
- Q = Volumetric Flow Rate (e.g., m³/s)
- A = Cross-sectional Area of the pipe (m²)
- v = Average Fluid Velocity (m/s)
Step-by-Step Calculation Logic
To use this calculation manually, you must perform the following steps, which our calculator handles automatically:
- Determine the Radius: Measure the internal diameter of the pipe and divide by 2 to get the radius (r = d / 2).
- Calculate the Area: Use the formula for the area of a circle: A = π × r².
- Standardize Units: Ensure the Area is in square meters and Velocity is in meters per second for a consistent result.
- Multiply: Multiply the Area by the Velocity to get the Flow Rate in cubic meters per second.
Practical Example
Let's say you have a water pipe with an internal diameter of 100 mm (0.1 meters) and the water is flowing at a velocity of 2 meters per second.
1. Calculate Area:
Radius = 0.1m / 2 = 0.05m
Area = 3.14159 × (0.05)² = 0.007854 m²
2. Calculate Flow (Q):
Q = 0.007854 m² × 2 m/s = 0.0157 m³/s
3. Convert to Liters:
Since 1 m³ = 1000 Liters:
0.0157 × 1000 = 15.7 Liters per second, or roughly 942 Liters per minute.
Why Flow Rate Matters
Accurate flow rate calculations are critical for sizing pumps, determining the efficiency of HVAC systems, and ensuring proper water pressure in residential plumbing. If the velocity is too high, it can cause pipe erosion and noise (water hammer). If it is too low, it may result in sediment buildup or insufficient delivery volume.
function calculateFlowRate() {
// 1. Get Input Elements
var diameterInput = document.getElementById("pipeDiameter");
var diameterUnit = document.getElementById("diameterUnit");
var velocityInput = document.getElementById("flowVelocity");
var velocityUnit = document.getElementById("velocityUnit");
// 2. Parse Values
var dVal = parseFloat(diameterInput.value);
var vVal = parseFloat(velocityInput.value);
// 3. Validation
if (isNaN(dVal) || isNaN(vVal) || dVal <= 0 || vVal * 60000)
var flowLpm = flowM3s * 60000;
// US GPM (1 m^3/s approx 15850.32 gpm)
var flowGpm = flowM3s * 15850.32314;
// 9. Display Results
document.getElementById("resM3s").innerHTML = flowM3s.toFixed(5) + " m³/s";
document.getElementById("resM3h").innerHTML = flowM3h.toFixed(2) + " m³/h";
document.getElementById("resLpm").innerHTML = flowLpm.toFixed(2) + " L/min";
document.getElementById("resGpm").innerHTML = flowGpm.toFixed(2) + " GPM";
// Format area appropriately (scientific notation if very small)
if(areaM2 < 0.0001) {
document.getElementById("resArea").innerHTML = areaM2.toExponential(4) + " m²";
} else {
document.getElementById("resArea").innerHTML = areaM2.toFixed(5) + " m²";
}
// Show container
document.getElementById("resultContainer").style.display = "block";
}