Calculate Pipe Diameter

Pipe Diameter Calculator

Determine the required internal pipe diameter based on flow rate and velocity.

Gallons per Minute (GPM) Cubic Meters per Hour (m³/h) Liters per Second (L/s)
Meters per Second (m/s) Feet per Second (ft/s)
function calculatePipeDiameter() { var flowRateInput = document.getElementById("flowRate").value; var flowRateUnit = document.getElementById("flowRateUnit").value; var velocityInput = document.getElementById("fluidVelocity").value; var velocityUnit = document.getElementById("velocityUnit").value; var resultDiv = document.getElementById("result"); var flowRate = parseFloat(flowRateInput); var velocity = parseFloat(velocityInput); if (isNaN(flowRate) || isNaN(velocity) || flowRate <= 0 || velocity <= 0) { resultDiv.innerHTML = 'Please enter valid, positive numbers for flow rate and velocity.'; return; } // — Unit Conversions to SI units (m³/s and m/s) — var flowRateInM3s; if (flowRateUnit === "gpm") { // 1 GPM = 0.0000630902 m³/s flowRateInM3s = flowRate * 0.0000630902; } else if (flowRateUnit === "m3h") { // 1 m³/h = 1/3600 m³/s flowRateInM3s = flowRate / 3600; } else if (flowRateUnit === "lps") { // 1 L/s = 0.001 m³/s flowRateInM3s = flowRate * 0.001; } var velocityInMs; if (velocityUnit === "fts") { // 1 ft/s = 0.3048 m/s velocityInMs = velocity * 0.3048; } else { // Already in m/s velocityInMs = velocity; } // — Calculation based on Q = A * v — // A = Q / v // A = π * (d/2)² = π * d² / 4 // Q / v = π * d² / 4 // d² = (4 * Q) / (π * v) // d = sqrt((4 * Q) / (π * v)) if (velocityInMs === 0) { resultDiv.innerHTML = 'Velocity cannot be zero.'; return; } var diameterInMeters = Math.sqrt((4 * flowRateInM3s) / (Math.PI * velocityInMs)); // — Convert result to common units — var diameterInMm = diameterInMeters * 1000; var diameterInInches = diameterInMeters * 39.3701; resultDiv.innerHTML = 'Required Internal Pipe Diameter:' + '' + diameterInMm.toFixed(2) + ' mm' + '(Equivalent to ' + diameterInInches.toFixed(2) + ' inches)'; }

Understanding Pipe Diameter Calculation

Properly sizing a pipe is crucial for the efficiency and longevity of any fluid transport system, whether it's for water distribution, HVAC, or industrial processes. An undersized pipe can lead to high velocities, causing excessive pressure drop, noise, and erosion. An oversized pipe is more expensive and can lead to low velocities, which may not be sufficient to transport suspended solids. This calculator helps you find the optimal internal pipe diameter based on the desired flow rate and fluid velocity.

The Core Formula

The calculation is based on the principle of the continuity equation for incompressible fluids:

Q = A × v

Where:

  • Q is the volumetric flow rate, or the volume of fluid passing through the pipe per unit of time.
  • A is the cross-sectional area of the pipe.
  • v is the average velocity of the fluid.

To find the diameter (d), we first rearrange the formula to solve for the area (A = Q / v). Since the area of a circle is A = π × (d/2)², we can substitute and solve for 'd':

d = √((4 × Q) / (π × v))

Our calculator performs these conversions and calculations for you, providing the required diameter in both millimeters and inches.

Practical Example

Let's say you need to design a water system that must deliver 200 Gallons per Minute (GPM). For a typical residential or light commercial copper pipe system, a recommended fluid velocity is around 2.5 meters per second (m/s) to minimize noise and erosion.

  1. Enter Flow Rate: 200 (unit: GPM)
  2. Enter Fluid Velocity: 2.5 (unit: m/s)
  3. Calculate: The calculator first converts 200 GPM to approximately 0.0126 m³/s.
  4. Apply Formula: d = √((4 × 0.0126) / (π × 2.5)) &approx; 0.080 m
  5. Result: The required internal diameter is 80.0 mm or about 3.15 inches. You would then select the next available standard pipe size, such as a 3.5-inch or 4-inch pipe, depending on availability and other system factors.

Key Considerations for Pipe Sizing

  • Fluid Type: The viscosity and corrosiveness of the fluid affect the recommended velocity. Water has different velocity limits than a slurry or a volatile chemical.
  • Pipe Material: Smoother pipes (like PVC or copper) can handle slightly higher velocities than rougher pipes (like concrete or old cast iron) before significant friction losses occur.
  • Pressure Drop: Higher velocities lead to greater pressure loss over the length of the pipe. For long pipe runs, you may need a larger diameter to maintain adequate pressure at the destination.
  • System Type: A suction line for a pump has different velocity requirements than a discharge line. Gravity-fed systems require careful sizing to ensure flow without pressure assistance.

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