Water Pipe Flow Rate Calculator

Water Pipe Flow Rate Calculator .wp-flow-calculator-container { font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif; max-width: 800px; margin: 0 auto; padding: 20px; border: 1px solid #e0e0e0; border-radius: 8px; background-color: #f9f9f9; } .wp-flow-calculator-header { text-align: center; margin-bottom: 25px; } .wp-flow-calculator-header h2 { color: #0073aa; margin-bottom: 10px; } .wp-flow-form-group { margin-bottom: 20px; background: #ffffff; padding: 15px; border-radius: 6px; box-shadow: 0 1px 3px rgba(0,0,0,0.1); } .wp-flow-form-group label { display: block; font-weight: 600; margin-bottom: 8px; color: #333; } .wp-flow-input-row { display: flex; gap: 10px; } .wp-flow-input-wrapper { flex: 2; } .wp-flow-select-wrapper { flex: 1; } .wp-flow-form-control { width: 100%; padding: 10px; border: 1px solid #ccc; border-radius: 4px; font-size: 16px; box-sizing: border-box; } .wp-flow-btn { display: block; width: 100%; padding: 15px; background-color: #0073aa; color: white; border: none; border-radius: 4px; font-size: 18px; font-weight: bold; cursor: pointer; transition: background-color 0.3s; } .wp-flow-btn:hover { background-color: #005177; } .wp-flow-results { margin-top: 25px; background-color: #ffffff; border: 1px solid #dcdcdc; border-radius: 6px; padding: 20px; display: none; } .wp-flow-result-item { display: flex; justify-content: space-between; align-items: center; padding: 12px 0; border-bottom: 1px solid #eee; } .wp-flow-result-item:last-child { border-bottom: none; } .wp-flow-result-label { color: #555; font-weight: 500; } .wp-flow-result-value { font-weight: bold; color: #0073aa; font-size: 18px; } .wp-flow-error { color: #d63638; margin-top: 10px; text-align: center; display: none; } .wp-flow-article { margin-top: 40px; line-height: 1.6; color: #333; } .wp-flow-article h3 { color: #23282d; margin-top: 30px; } .wp-flow-article h4 { color: #444; } .wp-flow-article p { margin-bottom: 15px; } .wp-flow-article ul { margin-bottom: 20px; padding-left: 20px; } .wp-flow-article li { margin-bottom: 8px; } @media (max-width: 600px) { .wp-flow-input-row { flex-direction: column; } } function calculateWaterFlow() { // Get inputs var diameterInput = document.getElementById('pipeDiameter').value; var diameterUnit = document.getElementById('diameterUnit').value; var velocityInput = document.getElementById('waterVelocity').value; var velocityUnit = document.getElementById('velocityUnit').value; var errorDiv = document.getElementById('flowError'); var resultDiv = document.getElementById('flowResults'); // Reset display errorDiv.style.display = 'none'; resultDiv.style.display = 'none'; // Validation if (diameterInput === "" || velocityInput === "") { errorDiv.innerText = "Please fill in both Pipe Diameter and Water Velocity fields."; errorDiv.style.display = 'block'; return; } var diameter = parseFloat(diameterInput); var velocity = parseFloat(velocityInput); if (isNaN(diameter) || isNaN(velocity) || diameter <= 0 || velocity < 0) { errorDiv.innerText = "Please enter valid positive numbers."; errorDiv.style.display = 'block'; return; } // Normalize Units to Metric (Meters and Meters/Second) for calculation // Convert Diameter to Meters var diameterInMeters = 0; if (diameterUnit === 'inch') { diameterInMeters = diameter * 0.0254; } else if (diameterUnit === 'mm') { diameterInMeters = diameter / 1000; } // Convert Velocity to Meters/Second var velocityInMetersSec = 0; if (velocityUnit === 'fps') { velocityInMetersSec = velocity * 0.3048; } else if (velocityUnit === 'mps') { velocityInMetersSec = velocity; } // Calculate Cross-Sectional Area (A = pi * r^2) // r = diameter / 2 var radius = diameterInMeters / 2; var area = Math.PI * Math.pow(radius, 2); // Calculate Flow Rate (Q = A * v) in Cubic Meters per Second var flowM3PerSec = area * velocityInMetersSec; // Convert Results to display units // 1 m3/s = 15850.3231 GPM var flowGPM = flowM3PerSec * 15850.3231; // 1 m3/s = 60000 Liters/min var flowLPM = flowM3PerSec * 60000; // 1 m3/s = 3600 m3/h var flowM3H = flowM3PerSec * 3600; // 1 m3/s = 35.3147 ft3/s (cfs) var flowCFS = flowM3PerSec * 35.3147; // Update UI document.getElementById('resGPM').innerText = flowGPM.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " GPM"; document.getElementById('resLPM').innerText = flowLPM.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " L/min"; document.getElementById('resM3H').innerText = flowM3H.toLocaleString(undefined, {minimumFractionDigits: 2, maximumFractionDigits: 2}) + " m³/h"; document.getElementById('resCFS').innerText = flowCFS.toLocaleString(undefined, {minimumFractionDigits: 4, maximumFractionDigits: 4}) + " ft³/s"; resultDiv.style.display = 'block'; }

Calculate volumetric flow rate based on pipe inner diameter and water velocity.

Pipe Inner Diameter (ID)

Inches (in) Millimeters (mm)

Water Velocity

Feet per Second (ft/s) Meters per Second (m/s)

Calculation Results

Gallons Per Minute (US) –

Liters Per Minute –

Cubic Meters Per Hour –

Cubic Feet Per Second –

Understanding Water Pipe Flow Rate Calculations

Determining the flow rate of water through a pipe is a fundamental task in plumbing, irrigation, and hydraulic engineering. The flow rate represents the volume of fluid that passes through a given cross-sectional area per unit of time. Understanding this metric helps ensure that pumps are sized correctly, irrigation systems provide adequate coverage, and residential plumbing maintains proper pressure.

The Flow Rate Formula

The most common method to calculate volumetric flow rate is using the Velocity-Area principle. The formula is expressed as:

Q = A × v

Q = Flow Rate (e.g., Cubic meters per second or GPM)
A = Cross-sectional Area of the pipe
v = Average velocity of the fluid

Step 1: Calculate the Area

First, you must determine the cross-sectional area of the pipe. Since pipes are circular, the area is calculated using the pipe's Inner Diameter (ID). It is crucial to use the inner diameter rather than the outer diameter, as the wall thickness of the pipe does not carry water.

Formula for Area: A = π × (Diameter / 2)²

Note: Ensure your diameter is converted to the same base units as your velocity (e.g., meters or feet) before calculating.

Step 2: Multiply by Velocity

Once you have the area, multiply it by the speed at which the water is traveling. Water velocity is often determined by the pressure driving the water and the friction losses within the pipe. In typical residential plumbing, water velocity is usually kept between 4 and 8 feet per second to prevent noise and pipe erosion.

Example Calculation

Let's say you have a pipe with an inner diameter of 2 inches and the water is flowing at 5 feet per second.

Convert 2 inches to feet: 2 ÷ 12 = 0.1667 feet.
Calculate Radius: 0.1667 ÷ 2 = 0.0833 feet.
Calculate Area: π × (0.0833)² ≈ 0.0218 square feet.
Calculate Flow (Q): 0.0218 sq ft × 5 ft/s = 0.109 cubic feet per second.
Convert to GPM: 0.109 × 448.83 ≈ 48.9 GPM.

Why Pipe Diameter Matters

Small changes in pipe diameter have a massive impact on flow rate. Because the formula involves squaring the radius, doubling the diameter of a pipe actually quadruples its cross-sectional area. This means a 2-inch pipe can carry four times as much water as a 1-inch pipe at the same velocity.

Common Units of Measurement

GPM (Gallons Per Minute): Standard in the US for plumbing and irrigation.
L/min (Liters Per Minute): Standard in metric countries and for smaller pumps.
m³/h (Cubic Meters per Hour): Common in industrial applications and large-scale water treatment.
ft/s (Feet per Second): Standard unit for velocity in the US.