Standard size for internal double door

im cutting through for an extension and plan on putting in some double French doors.

I don't have the budget for the doors at the moment so plan on cutting the hole and making good with a plan to add doors at a later date.

Is there a standard/recommended size or are they all different?

I guess if anything it's better to oversize and I can add thicker door linings?

Thanks

4' , 5' or 6' are the common standards.

It's a shame there isn't some kind of world wide network that you operate with a computer or something where you could type in a question or find out this kind of information.