Hazen-Williams Equation Calculator


Introduction to Hazen-Williams Equation

The Hazen-Williams equation is a widely acknowledged formula used in the field of hydraulic engineering, especially for calculating flow velocity and discharge in water supply systems. Developed by Allen Hazen and Gardner Stewart Williams in the early 20th century, this empirical formula has become a standard tool in the analysis of water flow in pipes.

Core Purpose of the Equation

The primary purpose of the Hazen-Williams equation is to estimate the velocity of water in a full-flowing pipeline. This calculation is crucial for designing water distribution systems, ensuring the pipes are adequately sized to meet the required flow rates without causing excessive pressure loss.

Formula and Parameters

Q = 0.278 C A D2.63 J0.54
  • Q = Flow rate (cubic meters per second, m³/s)
  • C = Hazen-Williams roughness coefficient
  • A = Cross-sectional area of the pipe (square meters, m²)
  • D = Diameter of the pipe (meters, m)
  • J = Hydraulic gradient (dimensionless)

Advantages and Applications

The Hazen-Williams equation is lauded for its simplicity and ease of use, making it an ideal choice for quick calculations without the need for complex computational resources. It is predominantly used in scenarios where water is at a moderate temperature, as the equation does not account for temperature variations. Typical applications include designing municipal water supply systems, fire suppression systems, and irrigation networks.


While the equation is highly useful, it has limitations. The most notable is its empirical nature, meaning it is derived from experimental data and may not accurately predict flow in all situations, especially for fluids other than water or for high temperatures.


In conclusion, the Hazen-Williams equation remains an essential tool in hydraulic engineering, offering a straightforward approach to solving real-world problems related to water flow in pipes. Its enduring relevance in the design and analysis of water distribution systems highlights its effectiveness and practical utility.