This is the kit we use to build our 42″ octagon Custom Stone Fire Pit. It measures 33″ across from flat edge to flat edge and can be custom sized from 12″ to 24″ in height. Comes complete with everything you need to build your fire pit except the cement board and finish materials.
To determine actual finished fire pit size:
For Width Add: 1/2″ per side for cement board, 2″ per side for stone veneer, 2″ per side for top material overhang. (ie: 27″+1″+4″+4″=36″)
For Height Add: 1/2″ for cement board, ?” for thickness of top material. (ie: 16″ frame height + 1/2″cement board + 2″ stone top = 18 1/2″)
These dimensions are approximate and will vary dependent on the actual material thicknesses you use