The invention relates to a method for determining the root mean square value of a vibration variable that is measured on a machine. A test measurement is carried out in order to obtain a test signal of the vibration variable with a test signal length; the influence of shortening the signal length of the test signal on the associated root mean square value is estimated and the relative deviation of the root mean square value emerging for a shortened signal length from the root mean square value emerging for the full test signal length is estimated therefrom as a function of the signal length to obtain a root mean square value error function; and a measurement of the vibration variable is carried out for determining the root mean square value. The measurement duration of this measurement is selected on the basis of the root mean square value error function.