Let me make this clear. There is NO set number of volunteer hours required for college admissions. Your high school may require a set number but colleges do not.
Instead you should focus on consistency and longevity in your volunteering. Two hours a week, every week for 3 years is much more impressive than 300 hours in the summer before senior year.
By worrying about number of hours you have in volunteering you miss the point. This is not an exercise in adding up hours where the person with the most hours wins. This is about helping people. and if you are really concerned about helping people and less concerned about how many hours you have, colleges will see that and reward you.
So how many volunteer hours do you need? 42. (If you don’t understand that answer you need to read more. Try Douglas Adams “The Hitchhiker’s Guide to the Galaxy.”