I would start at 5mg, work your way up from there. With no tolerance you'd be surprised how powerful oxycodone is. If you want to measure it get an oral syringe, crush the 30 mg into powder, dissolve it into 1 ml of water, suck it into the oral syringe through a cotton filter, then you know every 10 units is 3mg. Squirt it into your mouth or squirt it into a shot of water. If your into snorting then squirt each 10 units into its own little puddle on a plate, let it dry, then youll have 10 piles of relatively pure oxycodone at 3 mg a pile.
You can just eyeball it but that gets tricky when your doing 5mg at a time. If you find out 15mg is a good dose than just take a half pill, but start at 5. People with Broken bones get 5 mgs prescribed for pain, so although some people need 120mg to get real high don't underestimate it.