I'm not sure exactly but hear from friends that it's about 50% - bear in mind these would be very generalised claims from people working in Germany and trying to convince me I'm better off in Ireland. I think the last time I made a comparison with a friend living there a couple of years ago I was on 30k, she was on 38k but we essentially had the same take home salary.
However, it's hard to compare directly as living in Germany is so different and what you get for your money (tax or otherwise) varies quite a bit from here. Over there you'll pay lots of different taxes, can't remember them all now - there's income tax, church tax (which you will have to pay unless when you register over there you say you don't have a religion), old age care tax, social insurance, pension etc. There's an environmental tax on fuel too as far as I remember. But then generally accomodation is cheaper or at least no more expensive than Dublin (I'd know Frankfurt best so would be thinking of prices there) and often higher quality. And eating out, shopping etc are also often less expensive than here.