The period of a pendulum is the time taken for the pendulum to make a complete cycle.
In the absence of air resistance, the period of a pendulum is given by:

In the simulator below, it shows the number of complete oscillation and the time elapsed.
Simple Pendulum Simulation
Calculated Period: – seconds
Complete Oscillations: 0
Elapsed Time: 0.00 seconds
To practice finding the period of a pendulum, use this simulator here.