Use this if you know how much fluid (Volume) moved in a specific period (Time).
Liters (L)
Gallons (US)
Cubic Meters (m³)
Seconds
Minutes
Hours
Result: 0 Liters per second
2. Calculate by Pipe Diameter and Velocity
Use this if you know the internal diameter of the pipe and the speed of the fluid.
Flow Rate: 0 L/min
Cross-Sectional Area: 0 m²
Understanding Flow Rate: A Comprehensive Guide
Flow rate is a measurement of the volume of fluid (liquid or gas) that passes through a given surface per unit of time. It is a critical metric in plumbing, HVAC, irrigation, and industrial manufacturing.
How to Calculate Volumetric Flow Rate
The most basic way to calculate flow rate is using the volume/time formula:
Q = V / t
Q: Flow Rate
V: Volume of the fluid
t: Time elapsed
Example: If a 50-gallon tank fills up in 5 minutes, the flow rate is 50 / 5 = 10 gallons per minute (GPM).
Calculating Flow Rate in a Pipe
When dealing with pipes, flow rate depends on the cross-sectional area of the pipe and the velocity of the fluid moving through it. The formula is:
Q = A × v
A: Cross-sectional area (π × radius²)
v: Fluid velocity
This is essential for engineers to ensure that water pressure remains consistent across a network. If the pipe diameter decreases while the flow rate stays the same, the velocity must increase (Bernoulli's Principle).
Common Flow Rate Units
System
Units
Metric (SI)
Liters per second (L/s), Cubic meters per hour (m³/h)
Imperial (US)
Gallons per minute (GPM), Cubic feet per second (CFS)
function calculateVolFlow() {
var volValue = parseFloat(document.getElementById('flow_vol_value').value);
var volMultiplier = parseFloat(document.getElementById('flow_vol_unit').value);
var timeValue = parseFloat(document.getElementById('flow_time_value').value);
var timeMultiplier = parseFloat(document.getElementById('flow_time_unit').value);
var resultBox = document.getElementById('vol_result_box');
var resultVal = document.getElementById('vol_result_val');
if (isNaN(volValue) || isNaN(timeValue) || timeValue <= 0) {
alert("Please enter valid positive numbers for volume and time.");
return;
}
// Convert everything to Liters and Seconds
var totalLiters = volValue * volMultiplier;
var totalSeconds = timeValue * timeMultiplier;
var flowRate = totalLiters / totalSeconds;
resultVal.innerHTML = flowRate.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 4});
resultBox.style.display = "block";
}
function calculatePipeFlow() {
var diameterMM = parseFloat(document.getElementById('pipe_dia').value);
var velocity = parseFloat(document.getElementById('flow_vel').value);
var resultBox = document.getElementById('pipe_result_box');
var resultVal = document.getElementById('pipe_result_val');
var areaVal = document.getElementById('pipe_area_val');
if (isNaN(diameterMM) || isNaN(velocity) || diameterMM <= 0) {
alert("Please enter valid positive numbers for diameter and velocity.");
return;
}
// Convert diameter to meters
var diameterM = diameterMM / 1000;
var radius = diameterM / 2;
// Area = PI * r^2
var area = Math.PI * Math.pow(radius, 2);
// Flow Rate Q = A * v (Result in m3/s)
var flowRateM3s = area * velocity;
// Convert m3/s to Liters/minute (1 m3 = 1000L, 1 min = 60s)
var flowRateLmin = flowRateM3s * 1000 * 60;
areaVal.innerHTML = area.toLocaleString(undefined, {minimumFractionDigits: 6, maximumFractionDigits: 6});
resultVal.innerHTML = flowRateLmin.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2});
resultBox.style.display = "block";
}