Volumetric Flow Rate to Velocity Calculator

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Volumetric Flow Rate to Velocity Calculator :root { –primary-color: #0066cc; –secondary-color: #f0f7ff; –text-color: #333; –border-color: #ddd; –error-color: #dc3545; } body { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; line-height: 1.6; color: var(–text-color); margin: 0; padding: 20px; background-color: #f9f9f9; } .container { max-width: 800px; margin: 0 auto; background: white; padding: 30px; border-radius: 8px; box-shadow: 0 4px 6px rgba(0,0,0,0.1); } h1, h2, h3 { color: #2c3e50; margin-top: 0; } .calculator-box { background-color: var(–secondary-color); padding: 25px; border-radius: 8px; border: 1px solid var(–primary-color); margin-bottom: 30px; } .form-group { margin-bottom: 20px; } label { display: block; margin-bottom: 8px; font-weight: 600; } select, input { width: 100%; padding: 10px; border: 1px solid var(–border-color); border-radius: 4px; font-size: 16px; box-sizing: border-box; } .input-row { display: flex; gap: 15px; } .input-col { flex: 1; } button { background-color: var(–primary-color); color: white; border: none; padding: 12px 20px; font-size: 16px; font-weight: bold; border-radius: 4px; cursor: pointer; width: 100%; transition: background 0.3s; } button:hover { background-color: #0052a3; } #results { margin-top: 20px; padding: 20px; background-color: white; border-radius: 4px; display: none; border: 1px solid #ddd; } .result-item { margin-bottom: 15px; border-bottom: 1px solid #eee; padding-bottom: 10px; } .result-item:last-child { border-bottom: none; } .result-label { color: #666; font-size: 0.9em; } .result-value { font-size: 1.4em; font-weight: bold; color: var(–primary-color); } .hidden { display: none; } .article-content { margin-top: 40px; padding-top: 20px; border-top: 2px solid #eee; } .formula-box { background: #f8f9fa; padding: 15px; border-left: 4px solid var(–primary-color); font-family: monospace; margin: 15px 0; } table { width: 100%; border-collapse: collapse; margin: 20px 0; } th, td { border: 1px solid #ddd; padding: 10px; text-align: left; } th { background-color: #f2f2f2; }

Volumetric Flow Rate to Velocity Calculator

Round Pipe / Tube Rectangular Duct
m³/h L/min GPM (US) CFM (ft³/min) m³/s
mm inches cm meters feet

Results

Flow Velocity (Metric)
–
Flow Velocity (Imperial)
–
Cross-Sectional Area
–

Understanding Flow Rate and Velocity

In fluid dynamics, distinguishing between Volumetric Flow Rate and Flow Velocity is crucial for engineering applications ranging from HVAC duct sizing to industrial plumbing. While they are related, they measure different properties of the fluid in motion.

The Formula

The relationship between velocity, flow rate, and the cross-sectional area of the pipe or duct is defined by the Continuity Equation:

v = Q / A

Where:

  • v = Flow Velocity (how fast the particles are moving, typically m/s or ft/s)
  • Q = Volumetric Flow Rate (how much volume passes per time, e.g., m³/h, GPM)
  • A = Cross-Sectional Area of the conduit (m² or ft²)

How to Calculate Area (A)

The area depends on the shape of your conduit:

1. Round Pipe

For a circular pipe, the area is calculated using the internal diameter (D):

A = π × (D / 2)²

2. Rectangular Duct

For a rectangular duct, the area is simply the width multiplied by the height:

A = Width × Height

Common Unit Conversions

Since flow rates and dimensions are often provided in different units, conversion is the first step in any manual calculation. This calculator handles these conversions automatically.

Unit To Convert to SI (m³/s)
m³/h Divide by 3600
L/min (LPM) Divide by 60,000
GPM (US) Multiply by 0.00006309
CFM (ft³/min) Multiply by 0.0004719

Why Velocity Matters

Maintaing the correct velocity is vital. If velocity is too high, it can cause noise, erosion of pipe walls, and excessive pressure drop (head loss). If velocity is too low, suspended solids in the fluid may settle out, causing blockages, or the system may respond too slowly to temperature changes in HVAC applications.

Example Calculation

Suppose you have water flowing at 100 GPM through a 3-inch diameter pipe.

  1. Convert Flow: 100 GPM ≈ 0.006309 m³/s.
  2. Convert Diameter: 3 inches = 0.0762 meters.
  3. Calculate Area: A = π × (0.0762 / 2)² ≈ 0.00456 m².
  4. Calculate Velocity: v = 0.006309 / 0.00456 ≈ 1.38 m/s (or approx 4.5 ft/s).
function toggleShapeInputs() { var shape = document.getElementById('shapeSelect').value; var roundInputs = document.getElementById('roundInputs'); var rectInputs = document.getElementById('rectInputs'); if (shape === 'round') { roundInputs.classList.remove('hidden'); rectInputs.classList.add('hidden'); } else { roundInputs.classList.add('hidden'); rectInputs.classList.remove('hidden'); } } function calculateFlowVelocity() { // 1. Get Inputs var qRaw = parseFloat(document.getElementById('flowRate').value); var qUnit = document.getElementById('flowUnit').value; var shape = document.getElementById('shapeSelect').value; // Validation if (isNaN(qRaw) || qRaw <= 0) { alert("Please enter a valid positive flow rate."); return; } // 2. Convert Flow Rate (Q) to SI Unit: cubic meters per second (m³/s) var qSI = 0; switch(qUnit) { case 'm3s': qSI = qRaw; break; case 'm3h': qSI = qRaw / 3600; break; case 'lpm': qSI = qRaw / 60000; break; case 'gpm': // US Gallons per minute qSI = qRaw * 0.0000630901964; break; case 'cfm': // Cubic Feet per minute qSI = qRaw * 0.000471947443; break; } // 3. Calculate Area (A) in SI Unit: square meters (m²) var areaSI = 0; if (shape === 'round') { var diameterRaw = parseFloat(document.getElementById('diameter').value); var diameterUnit = document.getElementById('diameterUnit').value; if (isNaN(diameterRaw) || diameterRaw <= 0) { alert("Please enter a valid diameter."); return; } // Convert diameter to meters var diameterM = 0; if (diameterUnit === 'm') diameterM = diameterRaw; else if (diameterUnit === 'cm') diameterM = diameterRaw / 100; else if (diameterUnit === 'mm') diameterM = diameterRaw / 1000; else if (diameterUnit === 'inch') diameterM = diameterRaw * 0.0254; else if (diameterUnit === 'ft') diameterM = diameterRaw * 0.3048; // Area = pi * r^2 = pi * (d/2)^2 areaSI = Math.PI * Math.pow((diameterM / 2), 2); } else { // Rectangular var widthRaw = parseFloat(document.getElementById('width').value); var heightRaw = parseFloat(document.getElementById('height').value); var rectUnit = document.getElementById('rectUnit').value; if (isNaN(widthRaw) || widthRaw <= 0 || isNaN(heightRaw) || heightRaw <= 0) { alert("Please enter valid dimensions."); return; } // Convert dimensions to meters var widthM = 0; var heightM = 0; var factorToM = 1; if (rectUnit === 'cm') factorToM = 0.01; else if (rectUnit === 'mm') factorToM = 0.001; else if (rectUnit === 'inch') factorToM = 0.0254; else if (rectUnit === 'ft') factorToM = 0.3048; widthM = widthRaw * factorToM; heightM = heightRaw * factorToM; areaSI = widthM * heightM; } // 4. Calculate Velocity (v = Q / A) in m/s if (areaSI === 0) { alert("Calculated area is zero. Check dimensions."); return; } var velocitySI = qSI / areaSI; // m/s var velocityImperial = velocitySI * 3.28084; // ft/s // 5. Display Results document.getElementById('results').style.display = 'block'; document.getElementById('resVelocityMetric').innerHTML = velocitySI.toFixed(4) + " m/s"; document.getElementById('resVelocityImperial').innerHTML = velocityImperial.toFixed(4) + " ft/s"; // Show Area for reference var displayArea = areaSI < 0.01 ? areaSI.toExponential(4) : areaSI.toFixed(6); document.getElementById('resArea').innerHTML = displayArea + " m²"; }

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