Please enter valid positive numbers for all fields.
Estimated Flow Rate:0 GPM
Fluid Specific Gravity:1.0
Calculation Base:Hydraulic HP Formula
function calculatePumpFlow() {
// Get input elements
var powerInput = document.getElementById("motorPower");
var headInput = document.getElementById("totalHead");
var effInput = document.getElementById("efficiency");
var sgInput = document.getElementById("specificGravity");
var errorMsg = document.getElementById("error-message");
var resultArea = document.getElementById("result-area");
// Parse values
var hp = parseFloat(powerInput.value);
var head = parseFloat(headInput.value);
var efficiency = parseFloat(effInput.value);
var sg = parseFloat(sgInput.value);
// Validation
if (isNaN(hp) || isNaN(head) || isNaN(efficiency) || isNaN(sg) || hp <= 0 || head <= 0 || efficiency <= 0 || sg <= 0) {
errorMsg.style.display = "block";
resultArea.style.display = "none";
return;
}
errorMsg.style.display = "none";
// Logic: Water Horsepower Formula Rearranged for Flow (Q)
// Standard Formula: HP = (Q * H * SG) / (3960 * EfficiencyDecimal)
// Rearranged: Q = (HP * 3960 * EfficiencyDecimal) / (H * SG)
var efficiencyDecimal = efficiency / 100;
var constant = 3960; // Standard constant for US Gallons/min and Feet of Head
var flowRate = (hp * constant * efficiencyDecimal) / (head * sg);
// Update UI
document.getElementById("flowResult").innerHTML = flowRate.toFixed(2) + " GPM";
document.getElementById("sgResult").innerHTML = sg;
resultArea.style.display = "block";
}
How to Calculate Pump Flow Rate from Head
Understanding the relationship between pump head and flow rate is essential for sizing pumps correctly in industrial, agricultural, and residential applications. While the most accurate method involves consulting the specific "Pump Curve" provided by the manufacturer, you can estimate the flow rate using the fundamental Hydraulic Horsepower formula if the motor power and total dynamic head (TDH) are known.
The Relationship: Head vs. Flow
In centrifugal pumps, there is an inverse relationship between Head (pressure/height) and Flow (volume). As the vertical distance or pressure the pump must overcome increases (Head), the volume of liquid it can move decreases (Flow).
Total Dynamic Head (TDH): The total equivalent height that a fluid is to be pumped, taking into account friction losses in the pipe.
Flow Rate (Q): The volume of fluid moving through the pump per unit of time, typically measured in Gallons Per Minute (GPM).
The Calculation Formula
If you do not have the manufacturer's curve chart, but you know the horsepower of the motor driving the pump and the head it is pumping against, you can mathematically derive the estimated flow rate using the following physics equation:
Q = (3960 × HP × η) / (H × SG)
Where:
Q: Flow Rate in Gallons Per Minute (GPM).
3960: The conversion constant for US units.
HP: The Brake Horsepower applied to the pump shaft.
η (Eta): Pump Efficiency (typically 0.60 to 0.85 for standard centrifugal pumps).
H: Total Dynamic Head in feet.
SG: Specific Gravity of the fluid (Water = 1.0).
Example Calculation
Let's say you have a 5 HP motor driving a water pump. The pump needs to push water up a vertical elevation (plus friction loss) totaling 50 feet of head. The pump has a standard efficiency of 75%.
HP: 5
Head (H): 50 ft
Efficiency: 0.75
Specific Gravity: 1.0 (Water)
Using the formula:
Q = (3960 × 5 × 0.75) / (50 × 1.0)
Q = 14,850 / 50
Q = 297 GPM
This means that at 50 feet of head, utilizing 5 horsepower, the pump can theoretically move 297 gallons per minute.
Key Factors Affecting Results
Specific Gravity: If you are pumping a fluid heavier than water (like brine or slurry), the Specific Gravity will be greater than 1.0. This significantly reduces the flow rate a pump can achieve for a given horsepower.
Pump Efficiency: Pumps do not convert 100% of input energy into hydraulic energy. Energy is lost to heat, vibration, and friction. Older pumps may drop below 60% efficiency, while high-performance modern pumps can exceed 85%.