Definition: A kilolitre per hour (kl/h) is a unit of volumetric flow rate equal to 1,000 liters passing a point in one hour. It is used to measure relatively smaller volumes of liquid flow compared to kl/min or kl/s, but over a longer period.

History/origin: The unit stems from the litre, with 'kilo-' indicating 1000 litres. 'Per hour' denotes the flow rate over an hour. The development aligns with the need for standardised units to measure and control fluid transfer in various applications.

Current use: Kl/h is typically used in industrial processes, water treatment plants, and environmental monitoring where flow rates are lower and measured over longer durations. For example, measuring the flow rate of water in a small treatment plant or the flow rate of chemicals in a production line.