A cubic metre per second (m3s−1, m3/s, cumecs or cubic meter per second in American English) is the unit of volumetric flow rate in the International System of Units (SI) equal to that of a stere or cube with sides of one metre (39.37 in) in length exchanged or moving each second. It is popularly used for water flow, especially in rivers and streams, and fractions for HVAC values measuring air flow.