* The specific degree program: A PhD in Physics will likely require a different number of units than a PhD in Education or a Doctor of Medicine (MD).
* The institution: Different universities have different requirements.
* The student's background: Some programs may grant credit for prior coursework.
A doctoral program typically takes 4-7 years to complete, and the total number of units could range from 60 to 100+ units or even more, expressed in semester or quarter hours. It's best to check the specific requirements of the doctoral program you're interested in.