var currentMethod = 'vol';
function switchMethod(method) {
currentMethod = method;
var volInputs = document.getElementById('methodVolInputs');
var pipeInputs = document.getElementById('methodPipeInputs');
var btnVol = document.getElementById('btnMethodVol');
var btnPipe = document.getElementById('btnMethodPipe');
var resultBox = document.getElementById('flowResult');
// Reset Results
resultBox.style.display = 'none';
if (method === 'vol') {
volInputs.classList.remove('hidden');
pipeInputs.classList.add('hidden');
btnVol.classList.add('active');
btnPipe.classList.remove('active');
} else {
volInputs.classList.add('hidden');
pipeInputs.classList.remove('hidden');
btnVol.classList.remove('active');
btnPipe.classList.add('active');
}
}
function calculateFlowRate() {
// Base Unit will be Cubic Meters per Second (m3/s)
var flowRateM3S = 0;
var isValid = false;
if (currentMethod === 'vol') {
var volume = parseFloat(document.getElementById('volumeInput').value);
var volumeUnit = document.getElementById('volumeUnit').value;
var time = parseFloat(document.getElementById('timeInput').value);
var timeUnit = document.getElementById('timeUnit').value;
if (!isNaN(volume) && !isNaN(time) && time > 0) {
// Convert Volume to Cubic Meters (m3)
var volInM3 = 0;
if (volumeUnit === 'liters') volInM3 = volume / 1000;
else if (volumeUnit === 'gallons') volInM3 = volume * 0.00378541;
else if (volumeUnit === 'm3') volInM3 = volume;
else if (volumeUnit === 'ft3') volInM3 = volume * 0.0283168;
// Convert Time to Seconds
var timeInSec = 0;
if (timeUnit === 'seconds') timeInSec = time;
else if (timeUnit === 'minutes') timeInSec = time * 60;
else if (timeUnit === 'hours') timeInSec = time * 3600;
flowRateM3S = volInM3 / timeInSec;
isValid = true;
} else {
alert("Please enter valid positive numbers for Volume and Time.");
}
} else {
var diameter = parseFloat(document.getElementById('diameterInput').value);
var diameterUnit = document.getElementById('diameterUnit').value;
var velocity = parseFloat(document.getElementById('velocityInput').value);
var velocityUnit = document.getElementById('velocityUnit').value;
if (!isNaN(diameter) && !isNaN(velocity) && diameter > 0) {
// Convert Diameter to Meters
var diaInM = 0;
if (diameterUnit === 'mm') diaInM = diameter / 1000;
else if (diameterUnit === 'cm') diaInM = diameter / 100;
else if (diameterUnit === 'm') diaInM = diameter;
else if (diameterUnit === 'inch') diaInM = diameter * 0.0254;
// Calculate Area in m2 (A = pi * r^2) or (A = pi * (d/2)^2)
var radius = diaInM / 2;
var areaM2 = Math.PI * Math.pow(radius, 2);
// Convert Velocity to m/s
var velInMS = 0;
if (velocityUnit === 'ms') velInMS = velocity;
else if (velocityUnit === 'fts') velInMS = velocity * 0.3048;
// Q = A * v
flowRateM3S = areaM2 * velInMS;
isValid = true;
} else {
alert("Please enter valid numbers for Diameter and Velocity.");
}
}
if (isValid) {
// Conversions from m3/s
var valLPS = flowRateM3S * 1000;
var valLPM = valLPS * 60;
var valM3H = flowRateM3S * 3600;
var valGPM = valLPM / 3.78541; // US Gallons
// Display Results
document.getElementById('resGPM').innerHTML = valGPM.toFixed(2) + " gal/min";
document.getElementById('resLPM').innerHTML = valLPM.toFixed(2) + " L/min";
document.getElementById('resM3H').innerHTML = valM3H.toFixed(4) + " m³/h";
document.getElementById('resM3S').innerHTML = flowRateM3S.toFixed(6) + " m³/s";
document.getElementById('resLPS').innerHTML = valLPS.toFixed(3) + " L/s";
document.getElementById('flowResult').style.display = 'block';
}
}
Understanding the Flow Rate Formula
Whether you are designing a plumbing system, managing an irrigation network, or studying fluid dynamics, calculating the volumetric flow rate is a fundamental necessity. The flow rate measures the volume of fluid that passes through a specific point in a system per unit of time.
What is the Formula for Flow Rate?
There are two primary ways to calculate flow rate depending on the data you have available:
1. Using Volume and Time
If you know how much fluid was collected and how long it took, the formula is straightforward:
Q = V / t
Q = Volumetric Flow Rate (e.g., Liters/minute)
V = Volume of fluid collected (e.g., Liters, Gallons)
t = Time elapsed (e.g., seconds, minutes)
2. Using Pipe Area and Velocity
In closed pipe scenarios where you cannot measure the volume directly but know the pipe size and fluid speed, the formula is:
Q = A × v
Q = Volumetric Flow Rate (e.g., m³/s)
A = Cross-sectional Area of the pipe (m²)
v = Average Velocity of the fluid (m/s)
Note: To find the Area (A) of a round pipe, use the formula A = π × (d/2)², where d is the internal diameter of the pipe.
Example Calculation
Let's say you have a 2-inch diameter pipe (approx. 0.0508 meters) and water is flowing through it at a velocity of 1.5 meters per second.
First, calculate the radius: 0.0508m / 2 = 0.0254m
Calculate Area: π × (0.0254)² ≈ 0.0020268 m²
Calculate Flow Rate: 0.0020268 m² × 1.5 m/s ≈ 0.00304 m³/s
Converting 0.00304 m³/s leads to approximately 182.4 Liters per minute or roughly 48 GPM. Our calculator above automates these conversions instantly.
Why is Flow Rate Important?
Accurate flow calculations ensure that pumps are sized correctly, pipes do not suffer from excessive pressure drop due to high friction, and processes receive the exact amount of chemical or fluid required for operation. Inadequate flow can lead to system overheating, while excessive flow can cause water hammer and pipe erosion.