The website is http://ledcalc.com/
Its good but u have to make shure you no the power supply voltage is. Which will depend on what wire your using if you using a four pin molex. I can like give u some basic info of what i did for mine of you want coz it sounds like were doing/did the same thing.
The website is good as itl even tell you in what order you need to set the circuit up as well as how strong the resistor needs to be an how many per LED you may need.
When youve been on the website an put in you power supply voltage an the info on you LED's an clicked claculate. In the table that comes up below look at the 'Nearest higher rated resistor'. Which is the second box on the left. Thats the size resistor you will need. It'l make sense when you go on the website