# Hazen-Williams Flow Rate

on . Posted in Fluid Dynamics

Hazen-Williams flow rate is a widely used empirical formula for calculating the flow of water in a pipe.  It is commonly used in civil engineering and hydraulics for estimating the flow rate of water in a pipeline based on the characteristics of the pipe and the properties of the water.  The formula is particularly suited for water flow in municipal water supply and distribution systems.

The Hazen-Williams equation simplifies the calculation of flow rates compared to more complex methods like the Darcy-Weisbach equation. However, it is important to note that the Hazen-Williams equation is an empirical formula and may not be as accurate as more rigorous methods, especially for systems with high velocities or non-standard conditions.  It is commonly used for water supply systems where simplicity and ease of use are more critical than precision.

### Hazen-Williams Flow Rate formula

$$Q = C \; 0.285 \; d^{2.63} \; m^{0.54}$$     (Hazen-Williams Flow Rate)

$$C = Q \;/\; 0.285 \; d^{2.63} \; m^{0.54}$$

$$d = ( Q \;/\; C \; 0.285 \; m^{0.54} ) ^{1/2.63}$$

$$m = ( Q \;/\; C \; 0.285 \; d^{2.63} ) ^{1/0.54}$$

### Solve for Q

 Hazen-Williams coefficient, C pipe inside diameter, d hydraulic grade line, m

### Solve for C

 flow rate, Q pipe inside diameter, d hydraulic grade line, m

### Solve for d

 flow rate, Q Hazen-Williams coefficient, C hydraulic grade line, m

### Solve for m

 flow rate, Q Hazen-Williams coefficient, C pipe inside diameter, d
Symbol English Metric
$$Q$$ = flow rate $$ft^3 \;/\;sec$$ $$m^3\;/\; s$$
$$C$$ = Hazen-Williams coefficient, see below for values $$dimensionless$$
$$d$$ = pipe inside diameter $$in$$ $$mm$$
$$m$$ = hydraulic grade line slope $$dimensionless$$