This calculator helps you determine the appropriate pipe size based on your desired flow rate and a chosen fluid velocity. Selecting the correct pipe size is crucial for efficient fluid transport, preventing excessive pressure drop, and avoiding issues like water hammer.
Gallons Per Minute (GPM)
Liters Per Minute (LPM)
Cubic Meters Per Hour (m³/h)
Feet Per Second (FPS)
Meters Per Second (MPS)
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.input-section input[type="number"] {
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.input-section select {
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.result-section {
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function calculatePipeSize() {
var flowRateInput = document.getElementById("flowRate");
var flowRateUnitSelect = document.getElementById("flowRateUnit");
var fluidVelocityInput = document.getElementById("fluidVelocity");
var fluidVelocityUnitSelect = document.getElementById("fluidVelocityUnit");
var resultDiv = document.getElementById("result");
var flowRate = parseFloat(flowRateInput.value);
var flowRateUnit = flowRateUnitSelect.value;
var fluidVelocity = parseFloat(fluidVelocityInput.value);
var fluidVelocityUnit = fluidVelocityUnitSelect.value;
if (isNaN(flowRate) || isNaN(fluidVelocity) || flowRate <= 0 || fluidVelocity <= 0) {
resultDiv.innerHTML = "Please enter valid positive numbers for flow rate and velocity.";
return;
}
var flowRateCubicFeetPerMinute;
var fluidVelocityFeetPerSecond;
// Convert flow rate to Cubic Feet Per Minute (CFM)
if (flowRateUnit === "gpm") {
flowRateCubicFeetPerMinute = flowRate * 0.133681; // 1 GPM = 0.133681 cu ft/min
} else if (flowRateUnit === "lpm") {
flowRateCubicFeetPerMinute = flowRate * 0.0353147; // 1 LPM = 0.0353147 cu ft/min
} else { // m3h
flowRateCubicFeetPerMinute = flowRate * 35.3147; // 1 m³/h = 35.3147 cu ft/min
}
// Convert fluid velocity to Feet Per Second (FPS)
if (fluidVelocityUnit === "mps") {
fluidVelocityFeetPerSecond = fluidVelocity * 3.28084; // 1 MPS = 3.28084 FPS
} else { // fps
fluidVelocityFeetPerSecond = fluidVelocity;
}
// Calculate cross-sectional area in square feet
// Area = Flow Rate (cu ft/min) / Velocity (ft/min)
var velocityFeetPerMinute = fluidVelocityFeetPerSecond * 60;
var crossSectionalAreaSqFt = flowRateCubicFeetPerMinute / velocityFeetPerMinute;
// Calculate pipe diameter in feet
// Area = pi * (radius)^2 = pi * (diameter/2)^2 = pi * diameter^2 / 4
// Diameter^2 = 4 * Area / pi
// Diameter = sqrt(4 * Area / pi)
var pipeDiameterFeet = Math.sqrt((4 * crossSectionalAreaSqFt) / Math.PI);
// Convert diameter to inches for common pipe sizing
var pipeDiameterInches = pipeDiameterFeet * 12;
// Display results
resultDiv.innerHTML = "Required Pipe Diameter: " + pipeDiameterInches.toFixed(2) + " inches";
}
Understanding Pipe Sizing
Choosing the correct pipe size is a fundamental aspect of fluid systems engineering, impacting performance, efficiency, and longevity. The primary factors influencing pipe size are the flow rate of the fluid and the desired fluid velocity within the pipe.
Flow Rate
Flow rate, often expressed in gallons per minute (GPM), liters per minute (LPM), or cubic meters per hour (m³/h), quantifies the volume of fluid passing a point in a given amount of time. Higher flow rates generally necessitate larger pipes to accommodate the volume without excessive velocity.
Fluid Velocity
Fluid velocity, measured in feet per second (FPS) or meters per second (MPS), is the speed at which the fluid travels through the pipe. Maintaining an optimal velocity is crucial. Too low a velocity can lead to sedimentation and reduced system efficiency, while too high a velocity can cause excessive friction, pressure drop, noise, and erosion.
High Pressure/Velocity Applications: Can be higher, but requires careful consideration of pressure drop and material durability.
The Calculation
The relationship between flow rate, velocity, and pipe size is based on a simple principle: the cross-sectional area of the pipe must be large enough to allow the specified flow rate at the desired velocity.
The formula is derived from:
Flow Rate (Q): Volume per unit time.
Velocity (V): Distance per unit time.
Area (A): The cross-sectional area of the pipe.
The fundamental equation is Q = A × V. To find the required area (A), we rearrange this to A = Q / V.
Since the cross-sectional area of a pipe is circular (A = πr² = π(d/2)², where 'd' is the diameter), we can solve for the diameter:
d = √(4A / π)
This calculator converts your input units to a consistent system (cubic feet per minute and feet per second), calculates the required cross-sectional area, and then determines the corresponding pipe diameter in inches.
Example Calculation:
Suppose you need to pump 100 GPM of water at a desired velocity of 6 FPS.
Convert 100 GPM to Cubic Feet Per Minute (CFM): 100 GPM * 0.133681 cu ft/min per GPM = 13.3681 CFM.
Convert 6 FPS to Feet Per Minute (FPM): 6 FPS * 60 seconds/minute = 360 FPM.
Calculate the required Area: A = Q / V = 13.3681 CFM / 360 FPM = 0.03713 sq ft.
Calculate the Diameter in feet: d = √(4 * 0.03713 sq ft / π) ≈ √0.04726 ≈ 0.217 ft.
Convert Diameter to inches: 0.217 ft * 12 inches/ft ≈ 2.61 inches.
Therefore, for a flow rate of 100 GPM and a velocity of 6 FPS, you would need a pipe with an internal diameter of approximately 2.61 inches. In practice, you would typically select the next standard available pipe size (e.g., a 2.5-inch or 3-inch nominal pipe size, depending on the specific pipe schedule and internal diameter).