In hydrology, the discharge of a river is the volume of water transported by it in a certain amount of time. The unit used internationally is m³/s (cubic meters per second). For example, the average discharge of the Rhine river is 2200 m³/s. In the United States cfs, cubic feet per second, is commonly used. The discharge of a river can be estimated by taking the area of a cross-section of the river and multiplying it by the river's average velocity.