Pipe Size Calculation Based on Flow Rate

Pipe Diameter Calculator (Flow Rate Based)

Cubic Meters / Hour (m³/h) Liters / Minute (L/min) US Gallons / Minute (GPM) Cubic Meters / Second (m³/s)

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

Calculation Results:

Required Internal Diameter (ID):

0.00
Millimeters (mm)

0.00
Inches (in)

*Note: This is the exact calculated internal diameter. Choose the nearest standard pipe size with an internal diameter greater than or equal to this value.

function calculatePipeSize() { var Q_val = parseFloat(document.getElementById("flowRate").value); var Q_unit = document.getElementById("flowUnit").value; var V_val = parseFloat(document.getElementById("velocity").value); var V_unit = document.getElementById("velocityUnit").value; if (isNaN(Q_val) || isNaN(V_val) || Q_val <= 0 || V_val <= 0) { alert("Please enter valid positive numbers for flow rate and velocity."); return; } // Standardize Flow Rate to m3/s var Q_m3s = 0; if (Q_unit === "m3h") { Q_m3s = Q_val / 3600; } else if (Q_unit === "lmin") { Q_m3s = Q_val / 60000; } else if (Q_unit === "gpm") { Q_m3s = Q_val * 0.00006309; } else if (Q_unit === "m3s") { Q_m3s = Q_val; } // Standardize Velocity to m/s var V_ms = 0; if (V_unit === "ms") { V_ms = V_val; } else if (V_unit === "fts") { V_ms = V_val * 0.3048; } // Calculate Diameter D = sqrt((4 * Q) / (pi * V)) var D_meters = Math.sqrt((4 * Q_m3s) / (Math.PI * V_ms)); var D_mm = D_meters * 1000; var D_in = D_meters * 39.3701; document.getElementById("diameterMM").innerText = D_mm.toFixed(2); document.getElementById("diameterIN").innerText = D_in.toFixed(2); document.getElementById("pipeResultBox").style.display = "block"; }

Understanding Pipe Size Calculation

Selecting the correct pipe size is a critical step in hydraulic engineering and plumbing design. If a pipe is too small, velocity increases, leading to high pressure drops, noise, and potential erosion-corrosion. If a pipe is too large, the system becomes unnecessarily expensive and can cause issues with sediment buildup.

The Physics Formula

The relationship between pipe size, flow rate, and velocity is defined by the Continuity Equation for incompressible fluids:

Q = A × v

Where:

• Q is the Flow Rate (e.g., m³/s)
• A is the Cross-sectional Area of the pipe (πD²/4)
• v is the Flow Velocity (e.g., m/s)

To find the diameter, we rearrange the formula to:

D = √[(4 × Q) / (π × v)]

Recommended Velocities

When designing a system, the target velocity depends on the fluid and the application. Here are common industry standards:

Fluid / Application	Target Velocity (m/s)
Water (Suction Side)	0.5 – 1.5 m/s
Water (Delivery Side)	1.5 – 2.5 m/s
Compressed Air	6.0 – 15.0 m/s
Steam (Low Pressure)	20.0 – 30.0 m/s

Practical Example

Suppose you need to transport 15 m³/h of water on the delivery side of a pump. A common design choice is a velocity of 2.0 m/s.

1. Convert Flow Rate: 15 m³/h ÷ 3600 = 0.004167 m³/s.
2. Apply Formula: D = √[(4 × 0.004167) / (3.14159 × 2.0)].
3. Result: D ≈ 0.0515 meters or 51.5 mm.
4. Selection: You would likely select a standard 2-inch (DN50) pipe, which has a similar internal diameter.