Can anyone help me figure out this volume?

[boometro]

that box looks like 2.25cuft sealed and will be perfect for a pair of 10" subs.

[Jonathan Tyler Ecton-Rodriguez]

Is the middle section enclosed or open?

The middle is going to be closed and against the seat

[Jonathan Tyler Ecton-Rodriguez]

Also would it be better to cutout the area in front of the woofer so air can escape forwards or leave it closed under the seat?

If you're going to have air escaping it should be through a port otherwise you'll just have a leaky sealed box (nobody wants that). However, with the space being so small and limited, I don't think you'll have enough room to port it but I may be wrong. Maybe someone on here can design it so. For two twelves though, I can almost guarantee that you'll have to go sealed if you're able to fit the subs in there at all.

The box will be sealed but I was asking if the area above the woofer should be open, or sealed to the bottom of the seat. I left the difference in the picture, the woofer on the left would be open, the woofer on the right would be closed to the seat

[boometro]

leave the front edge open

[Triticum Agricolam]

You can use Sketchup to determine internal volume. If you make an object into a group it will give you its volume. See below:

Under "Entity Info" on the right side you can see it lists the volume for that group (40.5 cu in).

So to calculate the volume of your box you need to create shapes that fit inside your box. SketchUp gets a little finicky on calculating volume if the shape is too complex, you best bet is to create a series of simple shapes and add the volumes together.