Custom Fluid
Water (4°C)
Water (25°C)
Seawater
Engine Oil
Glycerine
Mercury
Kerosene
Unit: Cubic meters per second (m³/s)
Unit: Kilograms per cubic meter (kg/m³)
Unit: Meters per second squared (m/s²) – Default: Earth
Weight Flow Rate Result
0 N/s
function updateDensity() {
var preset = document.getElementById('fluidPreset');
var densityInput = document.getElementById('density');
if (preset.value !== 'custom') {
densityInput.value = preset.value;
}
}
function calculateFlowRate() {
// Get inputs
var volFlow = parseFloat(document.getElementById('volFlow').value);
var density = parseFloat(document.getElementById('density').value);
var gravity = parseFloat(document.getElementById('gravity').value);
// Validation
if (isNaN(volFlow) || isNaN(density) || isNaN(gravity)) {
alert("Please enter valid numerical values for all fields.");
return;
}
if (volFlow < 0 || density < 0) {
alert("Flow rate and density must be positive numbers.");
return;
}
// Calculation: W_dot = Q * rho * g
// Units: (m^3/s) * (kg/m^3) * (m/s^2) = (kg * m / s^2) / s = N/s
var weightFlowRate = volFlow * density * gravity;
// Secondary Calculation: Mass Flow Rate (m_dot = Q * rho)
var massFlowRate = volFlow * density;
// Display Results
var resultBox = document.getElementById('resultBox');
var mainResult = document.getElementById('mainResult');
var detailedResult = document.getElementById('detailedResult');
resultBox.style.display = 'block';
// Formatting numbers
mainResult.innerHTML = weightFlowRate.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 4}) + " N/s";
detailedResult.innerHTML =
"Calculation Breakdown:" +
"Mass Flow Rate (ṁ): " + massFlowRate.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 4}) + " kg/s" +
"Specific Weight (γ): " + (density * gravity).toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " N/m³";
// Scroll to result
resultBox.scrollIntoView({behavior: 'smooth', block: 'nearest'});
}
What is Weight Flow Rate?
The Weight Flow Rate is a fundamental concept in fluid dynamics and thermodynamics. It quantifies the weight of a fluid passing through a specific cross-sectional area per unit of time. Unlike volumetric flow rate (which measures space) or mass flow rate (which measures matter), weight flow rate accounts for the gravitational force acting on the fluid mass.
Engineers often use weight flow rate in systems where gravity plays a crucial role in the energy balance, such as in hydroelectric power plants, irrigation systems, and specific aerospace propulsion calculations. The standard SI unit for weight flow rate is Newtons per second (N/s).
The Weight Flow Rate Formula
To calculate the weight flow rate, you need to know the fluid's properties and how fast it is moving. The calculation generally links the volumetric flow rate with the specific weight of the fluid.
Ẇ = Q × ρ × g
Where:
Ẇ = Weight Flow Rate (N/s)
Q = Volumetric Flow Rate (m³/s)
ρ (rho) = Density of the fluid (kg/m³)
g = Acceleration due to gravity (approximately 9.81 m/s² on Earth)
Alternatively, if you already know the Mass Flow Rate (ṁ), the formula simplifies to:
Ẇ = ṁ × g
How to Use This Calculator
Our calculator is designed to assist engineers, students, and technicians in quickly determining the weight flow of various fluids.
Select Fluid (Optional): Choose a common fluid from the dropdown menu to automatically fill in the standard density. For example, selecting "Water (4°C)" will set the density to 1000 kg/m³.
Enter Volumetric Flow Rate (Q): Input the volume of fluid flowing per second in cubic meters (m³/s).
Verify Density (ρ): If you are using a custom fluid, manually enter its density in kg/m³.
Check Gravity (g): The calculator defaults to standard Earth gravity (9.80665 m/s²). Adjust this if you are calculating for a different altitude or planet.
Click Calculate: The tool will output the Weight Flow Rate in Newtons per second.
Real-World Example Calculation
Imagine a large water pump moving water at a rate of 0.5 m³/s. We want to find the weight flow rate to determine the load on the piping support structure.