Plumbing Flow Rate Calculator

by

Plumbing Flow Rate Calculator

Calculate GPM based on pipe diameter and water velocity

Common: 0.5″, 0.75″, 1.0″
Recommended: 5-8 FPS
Estimated Flow Rate
0.00 GPM
(0.00 Liters Per Minute)

Understanding Plumbing Flow Rates

In plumbing and hydraulic engineering, the flow rate is the volume of fluid which passes per unit of time. Determining the correct flow rate is critical for sizing pipes properly to ensure adequate water pressure and to prevent "water hammer" or pipe erosion caused by excessive velocity.

The Formula Used

This calculator uses the continuity equation for incompressible fluids:

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

To provide the result in Gallons Per Minute (GPM), we convert the area from square inches to square feet and then convert cubic feet per second to gallons per minute using the constant 448.83 (1 CFS ≈ 448.83 GPM).

Standard Velocity Guidelines

When designing a system, professional plumbers typically aim for specific velocity ranges:

Application Recommended Velocity
Residential Cold Water 5 – 8 FPS
Residential Hot Water 4 – 5 FPS
Service Lines Up to 10 FPS

Example Calculation

If you have a 1-inch pipe (ID) and a water velocity of 5 feet per second:

  1. Radius = 0.5 inches (0.04167 feet)
  2. Area = π × (0.04167)² ≈ 0.00545 sq. ft.
  3. Flow (CFS) = 0.00545 × 5 = 0.02725 cubic feet per second.
  4. Flow (GPM) = 0.02725 × 448.83 ≈ 12.23 GPM.
function calculateFlowRate() { var diameter = parseFloat(document.getElementById('pipeDiameter').value); var velocity = parseFloat(document.getElementById('flowVelocity').value); var resultDiv = document.getElementById('flowResult'); var gpmOutput = document.getElementById('gpmOutput'); var lpmOutput = document.getElementById('metricOutput'); if (isNaN(diameter) || isNaN(velocity) || diameter <= 0 || velocity <= 0) { alert('Please enter valid positive numbers for diameter and velocity.'); return; } // Calculation Logic // 1. Calculate Area in square inches: PI * (d/2)^2 var radius = diameter / 2; var areaInches = Math.PI * Math.pow(radius, 2); // 2. Convert Area to square feet var areaFeet = areaInches / 144; // 3. Flow rate in Cubic Feet per Second (CFS) var cfs = areaFeet * velocity; // 4. Convert CFS to Gallons Per Minute (GPM) // 1 cubic foot = 7.48052 gallons // 1 minute = 60 seconds var gpm = cfs * 7.48052 * 60; // 5. Convert GPM to Liters Per Minute (LPM) var lpm = gpm * 3.78541; // Display Results gpmOutput.innerHTML = gpm.toFixed(2) + ' GPM'; lpmOutput.innerHTML = '(' + lpm.toFixed(2) + ' Liters Per Minute)'; resultDiv.style.display = 'block'; }

Leave a Comment