Measuring device and method for measuring a size of a liquid

is formed measuring device for measuring a size of a liquid having and a measuring chamber (10, 28, 52) and at least one sensor (32, 60) in such a way to be arranged in a region of a liquid guide (2, 22), that the measuring chamber (10 , 28, 52) in the area of ​​the liquid guide (2, 22) accommodates at least a part of through the liquid guide (2, 22) flowing liquid and at least one sensor (32, 60) the size of the (in the measurement space 10, 28 , 52) detects absorbed liquid, and wherein (for calibration a calibration standard 8, 40) is provided, the arrangement thereof relative to the measuring chamber (10, 28, 52) by a position of a closure device (6, 34) of the liquid guide (2, 22) relative to said liquid guide (2, 22) is determined, wherein the calibration standard (8, 40) through the closure means (6, 34) is mechanically move, and wherein movement of said closure means (6, 34) the Flussigkeitsfuhrun g (2, 22) opens or closes.