Friction Loss Calculator

This friction loss calculator uses the Hazen-Williams equation to estimate the pressure or friction loss in pipes. The losses are calculated based on flow rates in circular pipes, the internal diameter of the pipe, the pipe length, and the type of pipe.

You can calculate friction loss in five easy steps:

  1. Select the pipe material (or manually input the Hazen Williams Coefficient)
  2. Input the internal diameter of your pipe
  3. Input the length of your pipe
  4. Input your pipe's flowrate
  5. Click the "Calculate" button and you will be given a result for the pipe's friction loss.
Friction Head Loss Calculator


With fluid flows, the viscosity of the fluid around the surface of a pipe or duct causes loss of pressure ("head"); this is what we mean by friction loss.

Hazen and Williams created an empirical formula to calculate pressure losses for liquids flowing through straight pipes. The formula below can calculate these losses over a given length of pipe.

hL = 10.67 * L * Q1.852 / C1.852 / d4.87   (SI Units)

In this equation, hL represents friction head loss (meters of H2O), L represents length of pipe (meters), d represents internal pipe diameter (meters), Q represents flow rate through the pipe (cubic meters per second), and C represents the Hazen-Williams coefficient, which will vary according to how smooth the internal surfaces of the pipe are.

The equation presupposes a fluid that has a kinematic viscosity of 1.13 centistokes; basically, water. Water's viscosity fluctuates in different temperatures, so errors may be present if the temperature is not 60°F (16°C). The pressure losses will be different according to how viscous a fluid is; however, this formula may be employed for all fluids that have a viscosity in the same range as water with preliminary calculations.

The Hazen-Williams Coefficient (C) fluctuates between around 60 and 160. The greater the coefficient, the smoother the pipe. C is dependent upon several elements; e.g., internal conditions on the pipe's surface, pipe age, and the effect of heat and chemical exposure over time. The coefficient will vary over a pipe's lifetime; as such, informed engineering judgements must be made when choosing appropriate values for the analysis of any given pipe system.

The Hazen-Williams method is accurate when water flows through pressurized pipes at a temperature of between 40° and 75°F (4° to 24°C). If the equation is employed at temperatures outside this range, a significant level of error will occur. This equation is frequently employed for the analysis of sprinkler and irrigation systems, domestic piping systems, and many other similar applications.

Example: You have a 100 m long pipe that has an internal diameter (D) of 25 cm. It is constructed of new unlined steel (C = 145) and discharges 40 L of water each second (L/s). Employ the Hazen-Williams equation to calculate the pipe's head loss.


hL = 10.67 * L * Q1.852 / C1.852 / d4.87

hL = 10.67 * 100 * 0.041.852 / 1451.852 / 0.254.87

hL = 1067 * 0.0025764 / 10065.921522 / 0.0011694

hL = 0.2335 m

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