Determine the axis that the object is rotating and measure the object's distance, r, from the point. This can be determined by measuring, however, this value is normally given in most physics problems dealing with angular momentum.
Identify the mass of the rotating object. Again, this value is usually given in the problem, however, the mass can be measured using a scale and reporting the value in kilograms.
Calculate the inertia of the object using the mass and radius. Inertia is the measure of an object's resistance to change in direction and is directly proportional to the mass and the radius of a rotating object. It is calculated by multiplying the mass of the object by the square of it's radius.
Inertia = Mass * Radius^2
Identify the angular velocity of the rotating object. Angular velocity is the product of the velocity and the angle between the velocity and momentum vector.
Angular velocity = velocity * sin(a), where a is the measure of the angle between the velocity and momentum vector.
Multiply the angular velocity by the inertia of the rotating object to obtain angular momentum. The value should be reported in units of kg*m^2/s.
Angular Momentum = Inertia*Angular Velocity