body {
font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
line-height: 1.6;
color: #333;
max-width: 800px;
margin: 0 auto;
padding: 20px;
}
.calculator-container {
background-color: #f8f9fa;
border: 1px solid #e9ecef;
border-radius: 8px;
padding: 30px;
margin-bottom: 40px;
box-shadow: 0 4px 6px rgba(0,0,0,0.05);
}
.calculator-title {
text-align: center;
color: #2c3e50;
margin-bottom: 25px;
font-size: 24px;
font-weight: 700;
}
.input-group {
margin-bottom: 20px;
}
.input-group label {
display: block;
margin-bottom: 8px;
font-weight: 600;
color: #495057;
}
.input-row {
display: flex;
gap: 10px;
}
.input-field {
flex: 2;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
font-size: 16px;
}
.unit-select {
flex: 1;
padding: 12px;
border: 1px solid #ced4da;
border-radius: 4px;
background-color: #fff;
font-size: 16px;
}
.calculate-btn {
width: 100%;
padding: 15px;
background-color: #007bff;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
font-weight: 600;
cursor: pointer;
transition: background-color 0.2s;
margin-top: 10px;
}
.calculate-btn:hover {
background-color: #0056b3;
}
.results-container {
margin-top: 25px;
padding: 20px;
background-color: #fff;
border: 1px solid #dee2e6;
border-radius: 4px;
display: none;
}
.result-item {
display: flex;
justify-content: space-between;
align-items: center;
padding: 10px 0;
border-bottom: 1px solid #eee;
}
.result-item:last-child {
border-bottom: none;
}
.result-label {
font-weight: 600;
color: #6c757d;
}
.result-value {
font-size: 20px;
font-weight: 700;
color: #28a745;
}
.article-content {
margin-top: 50px;
background: #fff;
}
.article-content h2 {
color: #2c3e50;
margin-top: 30px;
border-bottom: 2px solid #eee;
padding-bottom: 10px;
}
.article-content h3 {
color: #34495e;
margin-top: 20px;
}
.formula-box {
background-color: #eef2f7;
padding: 15px;
border-left: 4px solid #007bff;
font-family: monospace;
margin: 20px 0;
}
.info-table {
width: 100%;
border-collapse: collapse;
margin: 20px 0;
}
.info-table th, .info-table td {
border: 1px solid #ddd;
padding: 12px;
text-align: left;
}
.info-table th {
background-color: #f2f2f2;
}
@media (max-width: 600px) {
.input-row {
flex-direction: column;
}
}
function calculateMassFlow() {
// Get input values
var volFlowInput = document.getElementById("volFlow").value;
var volUnit = document.getElementById("volUnit").value;
var densityInput = document.getElementById("airDensity").value;
var densityUnit = document.getElementById("densityUnit").value;
// Validation
if (volFlowInput === "" || densityInput === "" || isNaN(volFlowInput) || isNaN(densityInput)) {
alert("Please enter valid numeric values for Flow Rate and Density.");
return;
}
var volFlow = parseFloat(volFlowInput);
var density = parseFloat(densityInput);
// Normalize Volumetric Flow to m³/s (SI Base)
var volFlowSI = 0;
if (volUnit === "m3s") {
volFlowSI = volFlow;
} else if (volUnit === "cfm") {
// 1 CFM = 0.000471947443 m³/s
volFlowSI = volFlow * 0.000471947443;
} else if (volUnit === "ls") {
// 1 L/s = 0.001 m³/s
volFlowSI = volFlow * 0.001;
} else if (volUnit === "cmh") {
// 1 m³/h = 1/3600 m³/s
volFlowSI = volFlow / 3600;
}
// Normalize Density to kg/m³ (SI Base)
var densitySI = 0;
if (densityUnit === "kgm3") {
densitySI = density;
} else if (densityUnit === "lbft3") {
// 1 lb/ft³ = 16.018463 kg/m³
densitySI = density * 16.018463;
}
// Calculate Mass Flow Rate in SI (kg/s)
// Formula: m_dot = Q * rho
var massFlowKgs = volFlowSI * densitySI;
// Convert Results
var massFlowLbMin = massFlowKgs * 132.277; // 1 kg/s approx 132.277 lb/min
var massFlowKgh = massFlowKgs * 3600;
var massFlowLbHr = massFlowLbMin * 60;
// Display Results
document.getElementById("resKgs").innerHTML = massFlowKgs.toFixed(4) + " kg/s";
document.getElementById("resLbMin").innerHTML = massFlowLbMin.toFixed(2) + " lb/min";
document.getElementById("resKgh").innerHTML = massFlowKgh.toFixed(2) + " kg/h";
document.getElementById("resLbHr").innerHTML = massFlowLbHr.toFixed(2) + " lb/hr";
// Show results container
document.getElementById("results").style.display = "block";
}
How to Calculate Air Mass Flow Rate
Understanding Air Mass Flow Rate is fundamental in fields such as HVAC engineering, aerodynamics, and thermodynamics. While volumetric flow rate (measured in CFM or m³/s) tells you how much space the air occupies as it moves, the mass flow rate tells you the actual amount of matter (mass) moving through the system.
This distinction is critical because the energy carrying capacity of air—whether for heating, cooling, or combustion—depends on the mass of the air molecules, not just the volume they occupy. Since air is compressible, its volume changes with temperature and pressure, but its mass remains constant.
The Air Mass Flow Rate Formula
To calculate the mass flow rate ($\dot{m}$), you need to know the volumetric flow rate ($Q$) and the density of the air ($\rho$). The fundamental equation is:
ṁ = Q × ρ
Where:
- ṁ (m-dot) = Mass Flow Rate (kg/s or lb/min)
- Q = Volumetric Flow Rate (m³/s or CFM)
- ρ (rho) = Air Density (kg/m³ or lb/ft³)
Why Air Density Matters
The most variable factor in this calculation is air density. Standard air density at sea level (15°C / 59°F) is approximately 1.225 kg/m³ or 0.0765 lb/ft³. However, density decreases as altitude increases or as temperature rises.
For example, in a hot engine intake or an HVAC system operating in Denver (high altitude), the air density is significantly lower than at sea level. If you only rely on volumetric flow (CFM) without accounting for density, you may overestimate the system's cooling or combustion capacity.
Common Unit Conversions
Engineering data often comes in mixed units. Here are common conversions helpful for air mass flow calculations:
| Measurement |
Conversion |
| Volume |
1 CFM = 0.000472 m³/s |
| Density |
1 lb/ft³ = 16.018 kg/m³ |
| Mass Flow |
1 kg/s = 132.28 lb/min |
Example Calculation
Let's say you have an HVAC duct moving 2,000 CFM of standard air.
- Convert Volume: 2,000 CFM × 0.000472 = 0.944 m³/s
- Determine Density: Standard air is approx 1.225 kg/m³
- Calculate: 0.944 m³/s × 1.225 kg/m³ = 1.156 kg/s
Using the calculator above simplifies these conversions and ensures accuracy for your engineering projects.