I would say 1.5 times stronger in terms of mg needed for a high but recreationally they are two very different substances for which purpose I find codeine infinitely superior. Codeine has a more sedating high which I prefer whilst DHC is less sedating but probably induces a slightly greater sense of well being.
Codeine induces a greater histamine reaction than DHC which is worth considering when debating if you should use an antihistamine or not. Beware some common antihistamines will inhibit CYP2D6 which prevents conversion of codeine to morphine. This is not something you have to consider DHC because unlike codeine, most of DHC's effects are caused by DHC itself and not its metabolites.