Planning a block fire pit
A round fire pit built from retaining wall blocks is one of the easiest backyard projects. The key numbers are how many blocks go around each course, how many courses you stack, and how much gravel goes under and inside the ring.
The formula
Blocks per course = π × (inside diameter + block depth) ÷ block length, rounded up
Using the circle through the middle of the blocks (inside diameter plus one block depth) accounts for the blocks fanning out around the ring. Tapered fire pit blocks fit tightly; rectangular blocks leave small V-shaped gaps at the back, which help the fire draw air.
Total blocks = blocks per course × number of courses
Example
A 36 in inside diameter with blocks 12 in long and 7 in deep: π × 43 ÷ 12 = 11.3, so 12 blocks per course. Four courses of 4 in blocks make a 16 in high wall with 48 blocks, plus 12 cap stones. The outside diameter is 50 in. A 4 in gravel base extending 6 in beyond the wall takes about 0.26 cu yd.
| Inside diameter | Blocks per course (12 × 7 in blocks) |
|---|---|
| 30 in | 10 |
| 36 in | 12 |
| 44 in | 14 |
| 48 in | 15 |
Building tips
- Most fire pits are 36 to 44 in inside and 12 to 18 in high: wide enough for a good fire, low enough to feel the heat.
- Dig 6 to 8 in, compact a gravel base and level the first course carefully: every course above follows it.
- Stagger joints between courses and glue the upper courses and caps with masonry adhesive rated for outdoor use.
- Line the inside with a steel fire ring, or firebrick, to protect the blocks from cracking; concrete blocks are not fire-rated.
- Place the pit at least 10 to 25 ft from the house, trees and fences, and check local fire rules and burn bans.