William Hazens Equation

Overview

Engineering reference data for William Hazens Equation in miscellaneous.

Key Formulas

Unit Conversion

$y = x \cdot k$

Multiply by conversion factor.

Linear Interpolation

$y = y_1 + \frac{(x - x_1)(y_2 - y_1)}{x_2 - x_1}$

Estimate between two known points.

Percentage

$p = \frac{\text{part}}{\text{whole}} \times 100\%$

Part as fraction of whole.

Variables

Symbol	Description	Unit
$x$	Input value	—
$y$	Output value	—
$k$	Conversion factor	—

Design Coefficient (c) Values by Pipe Material

Important Notes & Limitations

The Hazen-Williams equation is an empirical formula with specific constraints:

• Fluid Validity: The equation provides accurate estimates for fluids with a kinematic viscosity of approximately 1.1 cSt. It is considered acceptable for cold water at 60 °F (15.6 °C), which has a viscosity of 1.13 cSt.
• Temperature Limitation: The method is only valid for water at ordinary temperatures, typically between 40 °F and 75 °F (4 °C and 14 °C).
• Error in Hot Water: Using the equation for hot water (e.g., at 130 °F / 54.4 °C with a viscosity of 0.55 cSt) will result in significant error.
• Alternative Recommendation: For liquids or gases other than cold water, or for conditions outside the specified temperature range, use the Darcy-Weisbach equation.

Interactive Charts

References

• Original Source