.calculator-container {
max-width: 600px;
margin: 20px auto;
font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
border: 1px solid #e0e0e0;
border-radius: 8px;
box-shadow: 0 4px 12px rgba(0,0,0,0.05);
background: #fff;
}
.calc-header {
background: #0073aa;
color: white;
padding: 20px;
border-radius: 8px 8px 0 0;
text-align: center;
}
.calc-header h2 { margin: 0 0 10px 0; font-size: 24px; }
.calc-header p { margin: 0; opacity: 0.9; font-size: 14px; }
.calc-body { padding: 25px; }
.input-group { margin-bottom: 20px; }
.input-group label { display: block; font-weight: 600; margin-bottom: 5px; color: #333; }
.input-group input {
width: 100%;
padding: 10px;
border: 1px solid #ddd;
border-radius: 4px;
font-size: 16px;
box-sizing: border-box; /* Important for padding */
}
.input-group input:focus { border-color: #0073aa; outline: none; }
.input-group small { display: block; margin-top: 5px; color: #666; font-size: 12px; }
.calc-btn {
width: 100%;
padding: 12px;
background: #28a745;
color: white;
border: none;
border-radius: 4px;
font-size: 18px;
cursor: pointer;
transition: background 0.3s;
font-weight: bold;
}
.calc-btn:hover { background: #218838; }
.result-box {
margin-top: 25px;
padding: 20px;
background: #f8f9fa;
border-left: 5px solid #0073aa;
border-radius: 4px;
}
.result-box h3 { margin-top: 0; color: #333; border-bottom: 1px solid #ddd; padding-bottom: 10px; }
.result-row {
display: flex;
justify-content: space-between;
align-items: center;
padding: 10px 0;
border-bottom: 1px dashed #eee;
}
.result-row:last-child { border-bottom: none; }
.result-label { color: #555; font-weight: 500; }
.result-value { font-weight: bold; color: #0073aa; font-size: 18px; }
.result-info {
margin-top: 15px;
font-size: 12px;
color: #777;
font-style: italic;
text-align: center;
}
@media (max-width: 480px) {
.calc-header h2 { font-size: 20px; }
.result-value { font-size: 16px; }
}
function calculateFlow() {
// Get Inputs
var P = parseFloat(document.getElementById('pressurePsi').value);
var D = parseFloat(document.getElementById('diameterIn').value);
var Cd = parseFloat(document.getElementById('dischargeCoeff').value);
var SG = parseFloat(document.getElementById('specificGravity').value);
// Result Elements
var resGPM = document.getElementById('resGPM');
var resLPM = document.getElementById('resLPM');
var resVel = document.getElementById('resVel');
var resBox = document.getElementById('result-section');
// Validation
if (isNaN(P) || isNaN(D) || isNaN(Cd) || isNaN(SG) || P < 0 || D <= 0 || SG 0) {
velocityInPerSec = flowCubicInPerSec / areaSqIn;
}
// Convert Velocity to Feet per Second (1 ft = 12 in)
var velocityFtPerSec = velocityInPerSec / 12;
// — Display —
resBox.style.display = "block";
resGPM.innerHTML = flowGPM.toFixed(2) + " gal/min";
resLPM.innerHTML = flowLPM.toFixed(2) + " L/min";
resVel.innerHTML = velocityFtPerSec.toFixed(2) + " ft/s";
}
Understanding Pressure and Flow Rate
In fluid dynamics, the relationship between pressure and flow rate is fundamental for designing irrigation systems, hydraulic circuits, and industrial piping. While often confused, pressure acts as the potential energy that drives the fluid, while flow rate measures the actual volume of fluid moving over time. This calculator specifically determines the discharge flow rate through an orifice or nozzle given a specific pressure differential.
The Physics: Bernoulli's Principle
The calculation relies on a derivation of Bernoulli's equation for incompressible flow. The fundamental formula used to determine the flow rate ($Q$) through an orifice is:
Q = Cd × A × √(2 ΔP / ρ)
Where:
- $Q$: Volumetric Flow Rate
- $C_d$: Discharge Coefficient (accounts for energy losses and contraction of the jet)
- $A$: Cross-sectional Area of the orifice
- $\Delta P$: Pressure difference across the orifice
- $\rho$: Fluid Density
Key Inputs Explained
1. Pressure Differential (PSI)
This is not just the system pressure, but the difference in pressure between the inside of the pipe/tank and the outlet environment. If spraying into open air, this is simply the gauge pressure inside the pipe.
2. Orifice Diameter
The physical size of the opening. Small changes in diameter have a squared effect on the flow rate. Doubling the diameter typically quadruples the area, significantly increasing flow.
3. Discharge Coefficient ($C_d$)
Theoretical equations assume ideal flow. In reality, friction and turbulence reduce flow. The $C_d$ adjusts for this:
| Orifice Type |
Typical $C_d$ |
| Sharp-edged Orifice |
0.60 – 0.62 |
| Short Tube / Nipple |
0.80 – 0.82 |
| Smooth Well-rounded Nozzle |
0.97 – 0.98 |
4. Specific Gravity (SG)
This compares the fluid's density to water. Heavier fluids (higher SG) flow more slowly at the same pressure.
Water: 1.0
Gasoline: ~0.74
Diesel: ~0.85
Why is this important?
Engineers and technicians use this logic to size pumps, select nozzle tips for sprayers, and detect leaks. For example, if you know the pressure at a nozzle and the hole size, you can calculate exactly how many gallons per minute (GPM) are being dispensed, ensuring proper dosing for chemicals or efficient cooling for machinery.