This document gives guidelines to correct the measured air flow rate when measuring conditions are different from standard conditions. It applies to a power-law formula giving the air flow rate as a function of a pressure difference with an air flow rate coefficient, C, varying with temperature and pressure. This document applies to: passive elements of air distribution systems with a cross-section area that does not depend on pressure; volume flow rate (and not mass flow rate). This document is applicable to (but not limited to): EN 1507, Ventilation for buildings Sheet metal air ducts with rectangular section Requirements for strength and leakage; EN 1751, Ventilation for buildings Air terminal devices Aerodynamic testing of damper and valves; EN 12237, Ventilation for buildings Ductwork Strength and leakage of circular sheet metal ducts; EN 13141-1, Ventilation for buildings Performance testing of components/products for residential ventilation Part 1: Externally and internally mounted air transfer devices; EN 13141-2, Ventilation for buildings Performance testing of components/products for residential ventilation Part 2: Exhaust and supply air terminal devices; EN 13141-9, Ventilation for buildings Performance testing of components/products for residential ventilation Part 9: externally mounted humidity controlled air transfer device; EN 13141-10, Ventilation for buildings Performance testing of components/products for residential ventilation Part 10: humidity controlled extract air terminal device; EN 15727, Ventilation for buildings Ducts and ductwork components, leakage classification and testing. This document does not apply to: fans; air terminal devices with automatically controlled openings (variable openings).