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Mechanical Engineering2D

Pipe Diameter Calculator

Calculate required pipe diameter from flow rate and target velocity.

Inputs
Enter your values below

Typical: 1-3 m/s for liquids

Result
Required Diameter
—
Enter values and click Calculate
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Formula
√(4 × flow ÷ (π × velocity)) × 1000
Result unit: mm

D = √(4Q / (π × v)). Flow in m³/s, velocity in m/s; ×1000 converts m to mm.

Introduction

Calculate the minimum pipe inner diameter for a given flow rate and design velocity. Essential for hydraulic pipe sizing in process and utility systems.

How This Calculator Works

D = √(4Q / (π × v)). Flow in m³/s, velocity in m/s; ×1000 converts m to mm.

Step-by-step process:

  1. Enter your input values in the calculator above
  2. The engine converts all inputs to SI base units (meters, kg, Pa)
  3. The formula is evaluated: sqrt(4 * flow / (pi * velocity)) * 1000
  4. Result is formatted with the appropriate unit and precision

Calculation Example

For 50 m³/h at 2 m/s target velocity, minimum diameter is 94 mm. Standard DN100 (114.3mm OD, ~102mm ID) would work.

Inputs: flow=50, velocity=2
Result: 93.8 mm

Unit Conversion for Pipe Sizing

**Diameter units**

- 1 inch = 25.4 mm

- 1 mm = 0.03937 inch

- DN 50 = NPS 2 (nominal labels, not exact dimensions)

**Flow rate units**

- 1 m³/h = 0.2778 L/s = 4.403 US gpm

- 1 US gpm = 0.2271 m³/h

**Velocity units**

- 1 m/s = 3.28084 ft/s

When sizing, convert all inputs to one consistent unit system (metric or imperial) before applying the continuity equation Q = V × A.

Engineering Applications

  • •Process pipe sizing
  • •Hydraulic system design
  • •Plumbing design
  • •Pump suction sizing

Frequently Asked Questions

What standard pipe size should I select?

Round up to the nearest standard DN/NPS size. For example, if calc gives 94mm, select DN100 (4-inch).

What velocity should I design for?

Water discharge: 2-3 m/s; suction: <1.5 m/s; compressed air: 6-10 m/s; natural gas: 10-20 m/s.

What is the difference between nominal and actual pipe diameter?

Nominal pipe size (NPS/DN) is a label, not a dimension. Actual outside diameter is fixed per size, while wall thickness varies with schedule (Sch 40, Sch 80, etc.), so inside diameter = OD - 2 × wall thickness. Always use the actual ID for flow and velocity calculations.

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Engineering Disclaimer: Calculations are for reference and educational purposes only. Always verify results independently for engineering design. See full disclaimer.
Reviewed by: Industrial Engineering Team
References: ASME B31.3, ASTM A36, Perry's Chemical Engineers' Handbook