Unfortunately Bane, we are not in the business of getting you high... for the sake of harm reduction I will tell you that DHC is about twice as potent as codiene is considered to be on average, and it's NOT a prodrug, so it is more reliable
The standard conversion when switching, would be ~90mg, at most as a dosage unit
So 90mg DHC should be roughly equivalent to 20-30mg oxycodone in terms of potency, though how they effect you , both in the drug effects themselves (analgesic strength and, other effects you would likely seek) and strength, shall vary, and especially with Dhc's low, yet variable BA%; So I would take a small(er) test dose first, especially if you have not tried codiene, which it seems you have, still, please don't start with multiple tablets; Oh yeah, and if they are CR tablets, they shall last longer, though likely be less potent - well they won't hit as hard, potency shouldn't actually be effected though it shall feel that way
So use that a loose calculation, and would highly recommend starting with a low dose, and if everything is ok go from there. You can take more, usually not less
So am gonna have to close this. Luck and be safe