The Friction loss calculation deals with the flow of fluid through a pipe resisted by viscous shear stresses within the fluid and the turbulence that occurs along the internal pipe wall, which is dependent on the roughness of the pipe material. This resistance is termed pipe friction and is usually measured in feet or metres head of the fluid, which is why it is also referred to as the head loss due to pipe friction.

Friction loss is the consumption of energy. it is the loss of energy or 'head' that occurs in pipe flow due to viscous effects generated by the surface of the pipe. The friction loss In a uniform, straight sections of pipe, known as "major loss", is caused by the effects of viscosity, the movement of fluid molecules against each other or against the (possibly rough) wall of the pipe. The roughness of the pipe surface influences neither the fluid flow nor the friction loss. The faster that water moves over the roughness of a pipe wall, the greater the turbulence of the water flow and the greater the energy (pressure) loss. Thus careful considerations of friction loss is important for sizing pipes in an water system.

The friction loss affect a water supply due to the supply pipes being too small. The pressure of water flowing through a pipe is reduced due to the friction of the sidewall. This pressure reduction can affect the operation of a sprinkler system. Friction loss is also affected by the roughness of the inner surface of the pipe. The head loss in fluid flow is a friction loss (or skin friction), it is the loss of pressure or “head” that occurs in pipe or duct flow due to the effect of the fluid's viscosity near the surface of the pipe or duct.

The head loss is the pressure drop (due to friction) as a fluid flows through a pipe. Head losses represents how much pressure will be lost due to the orientation of the pipe system. As fluid flows through these bends, the pressure of the fluid flow decreases due to a change in the direction of the fluid.

The Pipe System Sizing maps hydraulic system and performs sizing algorithms, wherein it resizes and rebuilds piping system, edits system to coordinate layout and repeats analysis to produce completed system of critical paths of minimal pressure loss.