How long does it take for an ipod touch to charge?

My friend said it takes sometimes 20- 30 minutes for her's to charge but she also did say that it may take an hour to a few hours for an ipod to charge.
My 4g ipod touch only takes about 10-20 minutes to charge but if it is fully dead i would say probably only 30-45 minutes!!!!!! totaly not 3 hours