what is the flex pipe size needed in length for Volvo s40 2007?

We won't have measurements to share with you. Best bet is to order the flex pipe for your car from a parts store or dealer by vin number. If you want to go universal you can measure your existing flex pipe and order accordingly. Even though I work on my own cars I find it very affordable and much easier to have a dedicated exhaust shop do this kind of work. It normally very inexpensive. Alex