Is there a conversion rule for determing the strength of codeine compared to hydrocodone?

There are many rules: and they are all inaccurate, because the individual differences in how these drugs are metabolized are so great that odds are good any table is going to be wrong. However, in general, codeine is the least potent of all the opioids, with 60 mg being the equivalent of 5 mg of oxycodone and probably 7.5 mg of hydrocodone ON AVERAGE. This is if taken by mouth. IM codeine is more potent - about twice.