You'll struggle to get an equivalent dose that is accurate from DHC to Oxycodone. I think the best way to calculate it would be to convert both to Morphine and then find the equipotent dose.
If:
~100mg DHC = ~10mg Morphine
~5mg Oxycodone = ~10mg Morphine
Therefore:
~40mg of Oxycodone = ~80mg Morphine
And:
~80mg Morphine = ~800mg DHC
Thus:
~40mg Oxycodone = ~800mg DHC
However, as said, you'll have to take this converted dose with a pinch of salt, since it is calculated on several assumptions, and does not take cross-tolerance into account.
On a side note, I'm not really sure why you'd prefer to take DHC over Oxycodone for analgesic purposes alone?