How to Calculate Flow Rate of a Pipe

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Pipe Flow Rate Calculator

Calculate volumetric flow rate based on pipe diameter and velocity

Millimeters (mm) Centimeters (cm) Inches (in)
Meters per second (m/s) Feet per second (ft/s)

Calculation Results

Liters per Minute (LPM)

0

Cubic Meters per Hour (m³/h)

0

Gallons per Minute (US GPM)

0

Cubic Feet per Second (CFS)

0

Understanding Pipe Flow Rate Calculation

Calculating the flow rate of a pipe is a fundamental requirement in plumbing, civil engineering, and industrial process design. The flow rate represents the volume of fluid that passes through a specific cross-sectional area of the pipe per unit of time.

The Continuity Equation Formula

The most common method to determine the flow rate is using the area-velocity formula:

Q = A × v

Where:

  • Q: Volumetric Flow Rate
  • A: Cross-sectional Area of the pipe (π × r²)
  • v: Flow Velocity

Step-by-Step Calculation Example

Suppose you have a pipe with an internal diameter of 100 mm and the water is moving at a velocity of 1.5 meters per second (m/s).

  1. Convert Diameter to Meters: 100 mm = 0.1 meters.
  2. Calculate Radius: 0.1 / 2 = 0.05 meters.
  3. Calculate Area (A): π × (0.05)² = 0.007854 m².
  4. Calculate Flow Rate (Q): 0.007854 m² × 1.5 m/s = 0.011781 m³/s.
  5. Convert to Liters: 0.011781 × 1000 = 11.78 Liters per second, or approximately 706.8 Liters per minute.

Factors Affecting Flow Rate

While the formula above provides a theoretical value, real-world flow is influenced by several factors:

  • Pipe Friction: The roughness of the internal pipe wall slows down fluid near the edges.
  • Viscosity: Thicker fluids (like oil) flow differently than thinner fluids (like water).
  • Pressure: Higher pressure differentials typically increase velocity, thereby increasing flow rate.
  • Pipe Fittings: Elbows, valves, and reducers create turbulence and resistance, reducing the effective flow.
function calculateFlowRate() { var diameter = parseFloat(document.getElementById('pipeDiameter').value); var dUnit = document.getElementById('diameterUnit').value; var velocity = parseFloat(document.getElementById('flowVelocity').value); var vUnit = document.getElementById('velocityUnit').value; if (isNaN(diameter) || isNaN(velocity) || diameter <= 0 || velocity <= 0) { alert("Please enter valid positive numbers for diameter and velocity."); return; } // Convert diameter to meters var diameterInMeters; if (dUnit === 'mm') { diameterInMeters = diameter / 1000; } else if (dUnit === 'cm') { diameterInMeters = diameter / 100; } else if (dUnit === 'in') { diameterInMeters = diameter * 0.0254; } // Convert velocity to m/s var velocityInMS; if (vUnit === 'ms') { velocityInMS = velocity; } else if (vUnit === 'fps') { velocityInMS = velocity * 0.3048; } // Area Calculation: A = pi * r^2 var radius = diameterInMeters / 2; var area = Math.PI * Math.pow(radius, 2); // Flow Rate (Q) in m3/s var qM3S = area * velocityInMS; // Conversions var lpm = qM3S * 1000 * 60; var m3h = qM3S * 3600; var gpm = qM3S * 15850.32; // US Gallons per minute var cfs = qM3S * 35.3147; // Display Results document.getElementById('resLPM').innerHTML = lpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resM3H').innerHTML = m3h.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resGPM').innerHTML = gpm.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}); document.getElementById('resCFS').innerHTML = cfs.toLocaleString(undefined, {minimumFractionDigits: 4, maximumFractionDigits: 4}); document.getElementById('resultsArea').style.display = 'block'; }

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