Q2 (transitional flow rate)

The flow rate that divides a meter's range into a lower zone and an upper zone, each with its own maximum permissible error. Under ISO 4064 and OIML R 49, Q2 is 1.6 times Q1.

Between Q1 and Q2 a meter is allowed a wider error than above Q2. Knowing where Q2 falls shows how much of a household's low-flow use sits in the looser zone.