Identify the object’s shape and axis of rotation
Use the appropriate formula for that shape
For a point mass: (I = mr^2)
For multiple point masses: (I = sum mr^2)
For a solid rod about its center: (I = frac{1}{12}ML^2)
For a solid rod about one end: (I = frac{1}{3}ML^2)
For a solid disk or cylinder about its center: (I = frac{1}{2}MR^2)
For a thin hoop or ring: (I = MR^2)
For a solid sphere: (I = frac{2}{5}MR^2)
For a thin spherical shell: (I = frac{2}{3}MR^2)
Use the parallel axis theorem if the axis is shifted: (I = I_{cm} + Md^2)
Add the inertia of all parts if the object is composite
Use SI units: mass in kilograms, distance in meters, inertia in kg·m²