I have always gone by the 5 mg oxy = 7.5 mg hydro = 7.5 mg morphine (orally) = 45 mg codeine as a general rule of thumb as it is stated in many opioid equivalency charts, and seems to be fairly correct IME.
I have a tough time when comparing opiates. This is because they act differently than each other before they cross the blood brain barrier. This is more true than ever with different ROA's. I prefer IV heroin over any other opioid. Nothing else really works or compares to the feelings that it gives me.
This comparison has been beat to death here on BL, so you can find tons of information in previous threads on this topic.
Just type in "oxycodone hydrocodone" in the keyword(s) line on the search engine, and make sure that you have it set to 'search title only' in the dropdown option to the right.
This way you will find hundreds of posts on the subject instead of waiting for answers in this thread.
I will add that I find 20mg of hydrocodone to be about equal to 12.5mg of oxycodone.