This fire pit calculator counts the blocks per layer and in total for a round fire pit, the proper way โ around the wall centerline โ plus the base gravel. No sign-up. The working is shown under every number.
Quick example: a 36 in fire pit built 3 layers high from 12 in blocks needs 37 blocks plus 12 bags of base gravel โ $226.50 at the example prices.
| Item | Buy | Cost |
|---|---|---|
| Estimated total | $0.00 |
Curved walls need trapezoid or tapered blocks to close the joints; straight rectangular blocks leave wedge gaps on small pits โ go 36 in or bigger with those.
Estimate only โ not a guarantee. Mistakes are possible, so always check the quantities with your supplier or a builder before you buy or build.
Blocks are counted around the centerline of the wall โ the middle of the blocks, not the inside or outside edge. A 36 in inner diameter pit built with 4 in deep blocks has a 40 in centerline diameter, so each layer is ฯ ร 40 รท 12 in per block = 10.5, rounded up to 11 blocks. Three layers is 33 blocks, and 37 to buy with a 10% allowance for cuts and breakage. Published fire-pit guides use the same centerline method (a 36 in pit with 8 in blocks works out to 16 blocks per layer).
Use the centerline: (inner diameter + block depth) ร ฯ รท block length, rounded up. A 30 in pit with 12 in blocks needs 9 per layer; a 42 in pit needs 13 per layer. The table under the calculator shows the common sizes at this calculator's default settings.
Three layers of standard 4 in high wall blocks gives a 12 in high pit โ the most common height: high enough to contain the fire and seating-friendly, low enough to feel the heat. Four layers (16 in) suits a cooking pit or a raised look. This calculator counts any number of layers from 1 to 8.
Standard concrete wall blocks handle the outside of a pit, but direct flame makes concrete dry out and crack over time. For a pit you will use often, line the inside with fire bricks or a steel fire ring, keep a gravel base under the pit (this calculator includes it), and build on level ground well away from fences, decks and overhanging branches. Check local rules โ some areas restrict open fires or require a permit.
| Inner diameter | Block size | Blocks per layer | Blocks to buy |
|---|---|---|---|
| 30 in | 12 ร 4 in | 9 | 30 |
| 36 in | 12 ร 4 in | 11 | 37 |
| 36 in | 8 ร 4 in | 16 | 53 |
| 42 in | 12 ร 4 in | 13 | 43 |
Blocks are counted on the wall centerline (inner diameter + block depth). Base gravel for a 4 in pad under the pit is included in the calculator's list โ about 12 ร 0.5 cu ft bags for a 36 in pit.
These figures are planning estimates only โ not a guarantee and not professional advice. Mistakes are possible, including through an error in this calculator. Always check the quantities, sizes, spacings and depths with your supplier, a licensed builder, and your local building code before you buy materials or start work. The owner of this site accepts no responsibility or liability for any loss, cost, damage, injury, wasted material or failed inspection that results from using these estimates. Prices are examples to start from, not live prices or quotes.