For a simple pendulum (a point mass on a string) making small oscillations ($\sin \theta \approx \theta$): $T=2\pi \sqrt{\frac{L}{g}}$

• $L$: length of the string from the pivot to the center of mass of the bob.
• $g$: acceleration due to gravity. Crucially, the period is independent of the mass of the bob and the amplitude of oscillation (as long as the angle is small).