Concrete Fire Pit Calculator
Estimate concrete for a round poured or block-style concrete fire pit ring.
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Short answer
A typical 42-inch outer diameter fire pit ring with 5-inch walls and a 14-inch height needs about 5.5 cubic feet of concrete, or roughly 9 bags of 80 lb premix. Adding a solid floor increases the total, and heat-resistant materials matter more for a fire pit than for most other concrete projects.
Typical fire pit ring sizes
| Outer diameter | Wall thickness | Height |
|---|---|---|
| 36 in | 4–5 in | 12–14 in |
| 42 in | 5 in | 14 in |
| 48 in | 5–6 in | 14–16 in |
How to plan a concrete fire pit
- Check local fire codes for required clearance from structures, fences, and overhanging trees — often 10–25 feet.
- Choose an outer diameter and wall thickness, then enter them above to get volume and bag count.
- Use a heat-resistant aggregate or line the interior with firebrick or a metal fire ring insert — standard concrete can spall (crack and flake) from direct, repeated high heat.
- Add a few inches of gravel or sand at the base for drainage before pouring a floor, if included.
- Reinforce the ring with a light rebar hoop if it’s taller than about 12 inches, to resist cracking from heat cycling.
- Let the pit cure fully (28 days) before the first fire to avoid moisture-related spalling.
Worked example
- Outer / inner diameter
- 42 in outer, 42 – 2×5 = 32 in inner
- Ring cross-section area
- π/4 × (42² – 32²) = 581.2 in²
- Ring volume
- 581.2 × 14 in height / 1728 = 4.71 ft³, plus 10% waste = 5.18 ft³
- Bags (80 lb, 0.60 ft³ each)
- ceil(5.18 / 0.60) = 9 bags
Common mistakes
- Using standard structural concrete with no heat-resistant lining, which can crack and spall after repeated fires.
- Ignoring local clearance and burn ordinances, which vary widely by city and county.
- Building walls too thin for the height, resulting in a ring prone to cracking during heat cycling.
- Skipping drainage under the floor, letting water pool and freeze inside the pit over winter.
Assumptions
- Ring is modeled as a hollow cylinder: outer diameter minus twice the wall thickness gives the inner diameter.
- Standard concrete at roughly 150 lb per cubic foot; heat-resistant additive mixes may vary slightly in density.
- Bag yields follow manufacturer averages: 80 lb = 0.60 ft³, 60 lb = 0.45 ft³, 50 lb = 0.375 ft³, 40 lb = 0.30 ft³.
- Does not include a firebrick liner, metal insert, rebar, gravel base, or cap stones.
Frequently asked questions
Can I use regular concrete for a fire pit?
You can, but plain concrete is prone to spalling (cracking and flaking) from repeated direct high heat. Lining the interior with firebrick, a metal fire ring insert, or using a heat-resistant refractory mix protects the structure and extends its life.
How far should a fire pit be from my house?
Local codes vary widely, commonly requiring 10 to 25 feet of clearance from structures, fences, and overhanging branches. Always check your local fire code or ordinance before building.
Does a fire pit need a floor?
Not always — many designs sit directly on compacted gravel or sand for drainage. A solid concrete floor is optional and mainly used for a more finished look or added stability.