How do you convert your Reserve time to Active duty to see how many years you actually have?

Take your total points and divide by 360. That is your equivalent active YOS.
Yes, it's 360, not 365. No, I don't know why.

You can see your actual days served on the reserve portal of the HRC website. It's broken down between active duty days (basic training, school, so on) and inactive duty days (drill). It will give you a calculation of all your active duty days in years on the page but it doesn't add your inactive duty days. If you are thinking about going active duty you might want to talk to someone who has already gone reserve to active and see if those inactive days were recalculated towards their 20-year letter.