When controlling a process mean, we are interested with charts that can detect a shift inthe mean as soon as possible. The average run length of a control chart is the expected numberof samples or subgroups that would be obtained before a out-of-control signal is received. Inthis article we present exact formulas for the calculation of the average run length of the movingaverage chart. Tables and charts, provided in annexes, allow the choice of the adequate controlchart for a shift of fixed magnitude. It is clear that the moving average control chart is betterthan the Shewhart control chart and has an efficiency similar to EWMA and CUSUM chartswhile being as of simple use.