How Many Bricks for a Fire Pit?
A round fire pit is a stack of brick rings, so the count is bricks per ring times the number of courses. Here is the formula, a table by pit diameter (a 3 foot pit included), the course count for the height, and the fire brick to line the inside.
By the Calculate My Reno Team / Published
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A round fire pit is just a stack of brick rings, so the count is bricks per ring times the number of courses. The only wrinkle is that the bricks follow a curve, so you work off the circumference at the pit’s diameter, and the inside gets a separate fire brick liner to take the heat.
Skip the math for a square pit
For a square or rectangular pit, treat each side as a short wall and add them in the brick calculator - it handles the count and the mortar. The ring formula below is for a round pit, which the wall calculator does not curve around.
The ring formula
ring circumference = π × pit diameter (at the unit centreline)
units per ring = round( circumference ÷ unit face length )
courses = target height ÷ unit height (with joint)
total units = units per ring × courses
Measure the diameter at the middle of the wall, not the outer face, so the curve works out. Trapezoidal “fire-pit wall” stones are made to wedge into a circle; ordinary rectangular brick or block leaves small wedge gaps on the outside that the mortar fills.
Bricks by pit diameter
Outer diameter, using trapezoidal wall blocks (~7 in face) and standard 16 in block, per single ring:
| Pit outer diameter | Centreline circumference | Wall blocks / ring (~7 in) | Standard block / ring (16 in) |
|---|---|---|---|
| 30 in (2.5 ft) | ~85 in | ~12 | ~5 to 6 |
| 36 in (3 ft) | ~100 in | ~12 | ~6 to 7 |
| 42 in (3.5 ft) | ~115 in | ~14 | ~7 to 8 |
| 48 in (4 ft) | ~132 in | ~16 | ~8 to 9 |
Then multiply by the courses. Three to four courses (about 12 to 16 in high) is typical, so a 36 in pit in trapezoidal blocks is roughly 12 × 3 = 36 blocks.
Do not skip the fire brick
The inside face gets hot enough to spall ordinary clay brick or crack concrete block, so line the burn zone with fire brick (refractory brick) set in refractory mortar, not ordinary mortar. The liner is a smaller inner ring - for a 36 in outer pit the inner ring is around 24 in, about 8 to 9 fire bricks per course over 2 to 3 courses.
Worked example
A 36 in outer-diameter pit, trapezoidal wall blocks, 4 courses, plus a fire-brick liner:
- Centreline circumference: about 100 in.
- Units per ring at a 7 in face: 100 ÷ 7 = about 14, snug to 12 as the blocks wedge.
- Four courses: 12 × 4 = 48 wall blocks.
- Liner: about 8 fire bricks per course × 3 courses = 24 fire bricks.
Add a few spare - cutting and the odd breakage are normal. For the field walls around a patio the pit sits on, see how many bricks for a patio and how many bricks do I need.
Frequently asked questions
How many bricks do I need for a fire pit?
For a round pit, count the bricks in one ring, then multiply by the number of courses for the height. A typical 36 in (3 ft) outer-diameter pit takes roughly 10 to 12 standard blocks or trapezoidal wall stones per ring, and 3 to 4 courses to reach a 12 to 16 in height - so about 30 to 48 units. Line the inside with fire brick. The exact count depends on the unit size, so use the ring formula below.
How many bricks do I need for a 3 foot fire pit?
A 3 ft (36 in) outer-diameter pit has a ring circumference of about 113 in at the outer face, or nearer 100 in at the block centreline. With trapezoidal fire-pit wall blocks (about 7 in face) that is roughly 12 blocks per ring; with standard 16 in blocks it is about 6 to 7 per ring. Three to four courses gives a usable height, so plan on about 24 to 48 units plus the fire brick liner.
How many fire bricks do I need for a fire pit?
The fire brick lines the inside face of the pit, so it is its own smaller ring. For a 36 in outer pit the inner diameter is around 24 in, a circumference of about 75 in; with 9 in fire bricks laid on edge that is about 8 to 9 fire bricks per course, and 2 to 3 courses up the burn zone - so roughly 18 to 27 fire bricks. Fire brick handles the heat that would crack ordinary brick or block.
How many courses high should a fire pit be?
Most fire pits are 3 to 4 courses, giving a wall about 12 to 18 in high above the ground. Lower than that and the fire feels exposed; much higher and you lose the heat and the view. Divide your target height by the unit height (with the joint) to get the course count - a 16 in pit in 8 in block is two courses above grade plus a base course.