Cubic metre per second or cubic meter per second in American English (symbol m3s−1 or m3/s) is the unit of volumetric flow rate in the International System of Units (SI). It corresponds to the exchange or movement of the volume of a cube with sides of 1 m in length (a cubic meter, originally a stere) each second. It is popularly used for water flow, especially in rivers and streams, and fractions for HVAC values measuring air flow. The term cumec is sometimes used as an acronym for full unit name, with the plural form cumecs also common in speech. It is commonly used between workers in the measurement of water flow through natural streams and civil works, but rarely used in writing. Data in units of m3s−1 are used along the y-axis or vertical axis of a flow hydrograph, which describes the time variation of discharge of a river (the mean velocity multiplied by cross-sectional area). A moderately sized river discharges in the order of 100 m3s−1.

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