Fire is 40” diameter. So fire extends 20” from center. Fire pit is 12’ diameter so back of pit is 6’ from center. Fire extends 4’4” from back of pit. Chairs are 34” deep so fire extends within 52-34=18” from front of chair, assuming you can get chair back to back of pit. You can’t because it’s an arc. So figure you’re going to lose 4” on back of chair. Assume further that people’s legs are 5” proud of front of chair st knee, 14” proud at foot. That’s 9” from edge of fire to knee and 0” from edge of fire to toe. This doesn’t account for a further course of bricks around edge of fire if beyond the 40” diameter of fire. I’d say that’s a no go. For example when one person is seated you definitely couldn’t have another person pass between them and the fire comfortably. This also assumes that wind will not blow flames outside the 40” pit. Also your guests couldn’t extend their legs out at all. They’d have to sit with the sole down on the ground with no room to extend. Widen that pit 4’. More on reddit.com

Volume of a cylinder = Pi x radius squared x height. 3.14 x (38 x 38) x 5 = 22671 cubic inches or 13.12 cubic feet. Spot on, old chap. More on reddit.com

Fire pit alone $2000-$2500 Paver patio 200 sqft $2400-$3000 Seating walls are waste of money -sitting on concrete is uncomfortable after awhile -fire too hot, too cold can’t move around If you want do it on a budget I recommend hiring some one to pour you a concrete slab do exposed aggregate or stamp to fancy it up Do a stand alone smokeless firepit I use Breeo on my projects Get some nice lawn chairs More on reddit.com

30" strikes me as pretty small, but I think it more depends on what size fire you want than how many people. You don't have to sit so close that you are touching it. More on reddit.com