How can calculate productivity over a workshop?

Productivity / Capability can be easily measured if we know rated speed / capacity of any machine so that we simply multiply with available hours / earned hours. Well in workshop similar concept but in a slightly different way. Here basically time based studies can be measured for each task. Total time taken to complete a task (actual time) T1  versus expected time (theoratical time)  T2 to calculate efficiency simply T1 divided by T2 multiply by100.