ISO 6358-3:2014 specifies a method that uses a simple numerical technique to estimate without measurements the overall flow-rate characteristics of a system of components and piping with known flow-rate characteristics.

The formulae used in ISO 6358-3:2014 describe the behaviour of a compressible fluid flow through a component for both subsonic and choked flows.

ISO 6358-3:2014 also provides methods to obtain equivalent flow-rate characteristics for components whose flow-rate characteristics differ from those defined in ISO 6358.