How many blocks for a 36 inch fire pit?

A 36 in bowl is the classic backyard size: big enough for a real fire, small enough that people can sit close. Many steel fire ring inserts are sold in this size.

Why the outside size matters

Tapered blocks fit together along their angled sides with their wide faces on the outside, so the count comes from the outside circle. A 36 in inside diameter with 7 in deep blocks makes an outside diameter of 50 in — a circumference of 157 in. With 12 in faces that is 13.1 blocks; the extra tenth of a block disappears into the joints, so 13 per course closes the ring. Blocks with a different face length change the count: 10 in faces need 16 per course, 8 in faces need 20.

Three courses of 4 in blocks build a 12 in wall, comfortable for resting feet on. Some kits use two courses of taller blocks plus a cap.

Bricks instead

With bricks laid lengthwise, the count comes from the inside circle: 3.1416 × 36 in ÷ 7⅝ in is about 15 bricks per course (variant below), and at 2¼ in tall you need about five courses for a 12 in wall — 75 or so in all. Larger pits are on how many blocks for a 48 inch fire pit, and a square version in cinder block on how many cinder blocks for a fire pit.