One condom is enough.
There is no need to use more than one and if anything, that would make you less protected because the friction between the condoms can cause tears.

Use one condom, spermicide (sold where condoms are), and your girlfriend should be on birth control as well.

No, don't do that!!

Marianne has it right- one condom, plus spermicide, or hormonal birth control. Or both.

my girl friend want to get pregnant, but i dont want.now she have agree not to. but i believe she want to take me on awere.what to i do?she wouldnt want me use condom

how old are you?

if your not wanting to have sex in order to have a baby just tell her.
dont just say well ok and go along and have sex without a condom.
tell her if you dont use protection your not having sex and thats final.

and if she wont listen to you when you say that, tell her parents what she is wanting to do.
one way or the other it will stop her from this want of pregnancy..it sounds like shes young too.