Transformer Math?

[KFC]

After see make: magazine's Joule Thief I want to "make: a toroid transformer":D. Does anyone know any link to a comprehensive explanation on transformer calculations(like turns of primary, or secondary coil for upping or downing voltage/amperage)? I think some the the variables are primary wire turns, primary voltage, primary amperes, secondary wire turns, and secondary resistance load?

[big314mp]

It's basically (ignoring coupling issues) the ratio of the turns. Think of it as a gear box for electricity. So if you have 10 turns on the primary, and 100 on the secondary, your current will decrease 10x and your voltage will increase 10x.