How many calories?

Can somebody please help me to establish how many calories I should be eating in order to lose weight?? I am 5'2" and 118lbs. I am hoping to lose 6lbs. To be honest I would like to lose it quickly enough, max within a four week period as I am going on hols then and would'nt mind even being a few pound under. Im currently following a 1200 a day and have had mixed results although I went completley AWOL this weekend so doubt if I will lose this week. HELLLLLP!