Hi can any one tell me how to mix my hair colour!

I have bought a colour which 12.0 and was recommended to get the 40 vol developer, but no one told me how much to use of each item.

Do I use the whole colour tube to 1 part developer or what?

PLEASE HELP

Usually it is 2 ounces of developer for one small bottle of toner or tube. The 40 vol developer is quite harsh for you to use unless you are going to be super super blonde or almost white hair. The most I've ever used was a 30 vol developer on my hair. After you color your hair be sure to use a very good conditioner so your hair ends do not dry out.