subwoofer box dimensions

I am having a hard time figuring out what the dimensions of a sealed box should be. I am planning on putting in 2 12" Infinity Reference 1250w Subwoofers at 300w RMS each. I pretty much know the basics of how to go about building a box, i'm just not sure how to get the dimensions. I haven't measured out my trunk space but it's a fairly large trunk so i'm sure it will be able to accomodate any decent sized box. Any help is appreciated.

Thanks for the info. Do you have any idea on the exact size I should cut the holes? On the infinity site, it says the cutout diameter for the sub is 11 3/16". Is that the size I should cut the holes or is it something else?

I would go by the size Infinity gives you.

Yes, "cutout" is the exact size you should cut the hole.  You don't want to make it too large because there won't be enough wood to screw into, and if too small the woofer won't settle into it.  The woofer should set into the hole with just the slightest amount of play to all sides.Build the box so that it performs well in the worst case scenario and, in return, it will reward you at all times.

Thanks for all the help. So basically, it doesn't really make that much of a difference what the dimensions are, as long as box is around 2.5 cubic feet in volume? Also do you recommend in the middle since i'm putting in 2 drivers? I calculated it out and if I make a box thats 35"X13"X13" with 3/4" fiberboard and put in a divider, the total volume should come out to about 2.508 cu. ft. Does that sound like it would work? I have some rough drawings if you would like to see them.

Sounds like it should be just fine. Sealed boxes can be pretty forgiving if the air space isn't exactly right, but what you have come if with be good to go. And yes, I would go with the divider in the middle if it was me, makes the box more sturdy as well.

Ok, thanks for your help everyone.