Fire pit block calculator
Pick the shape and the unit you are using, enter the inside size and the block dimensions, and see how many you need per course and in total.
Enter your measurements
More options: Spares
- Per course
- 13 blocks
- Outside diameter / width
- 50 in
- Wall height (dry-stacked)
- 12 in
Outside circle 3.1416 × 50 in ÷ 12 in face = 13 blocks per course
× 3 courses + 5% spares = 41 blocks
Quick answers for common sizes
| Example | Answer |
|---|---|
| How many blocks for a 36 inch fire pit | 13 blocks per course; 41 blocks for 3 courses with spares |
| How many blocks for a 48 inch fire pit | 17 blocks per course; 54 blocks for 3 courses with spares |
| How many cinder blocks for a fire pit | 12 blocks per course (3 per side); 24 blocks for 2 courses |
Blocks by inside size (unit and courses as above)
| Inside diameter or width | Per course | Blocks to buy | Outside diameter / width |
|---|---|---|---|
| 30 in | 12 blocks | 38 blocks | 44 in |
| 36 in | 13 blocks | 41 blocks | 50 in |
| 42 in | 15 blocks | 48 blocks | 56 in |
| 48 in | 17 blocks | 54 blocks | 62 in |
| 60 in | 20 blocks | 63 blocks | 74 in |
A fire pit wall is a ring of units, so the count per course is the distance around the ring divided by the length of each unit. Which distance you use depends on the unit’s shape:
- Tapered wall blocks (the wedge-shaped landscape blocks sold for walls and fire pits) touch along their sides, so their wide front faces line the outside circle: per course = 3.1416 × outside diameter ÷ face length.
- Bricks touch at their inside corners and open up on the outside: per course = 3.1416 × inside diameter ÷ length.
- A square pit of cinder blocks laid pinwheel-style needs the same whole number of blocks on each side, so a course is always a multiple of 4: inside width = blocks per side × block length − block depth.
outside diameter = inside diameter + 2 × unit depth wedge blocks: per course = 3.1416 × outside diameter ÷ face length bricks: per course = 3.1416 × inside diameter ÷ length square: per course = 4 × blocks per side total = per course × courses
As a real-world check, Allan Block’s fire pit how-to uses 28 of its York blocks per course to make a ring about 81 in across. Manufacturer fire pit kits list their own counts — if you buy a kit, follow its sheet.
Worked examples
- How many blocks for a 36 inch fire pit — the most popular size, with tapered wall blocks.
- How many blocks for a 48 inch fire pit — a bigger ring, and how the outside grows.
- How many cinder blocks for a fire pit — a square pit from 8×8×16 blocks.
Build notes
- Dig out a few inches and set the first course on compacted gravel so it stays level; the gravel base calculator sizes it.
- Leave small gaps in the bottom course or add a drain layer so rain doesn’t pool in the bowl.
- Glue the top course or caps with masonry adhesive, or set them in mortar.
- Line the bowl with a steel fire ring or firebrick. Regular concrete block and brick can crack or spall when exposed to direct, repeated fire.
What you’ll need
- Steel fire pit ringMid-range price
A heavy steel liner set inside a block fire pit keeps direct flame off the wall units.
See options on Amazon (opens in a new tab) - Masonry construction adhesiveBudget price
Locks the top course or caps of a dry-stacked fire pit or garden wall. Not a substitute for mortar where a wall needs it.
See options on Amazon (opens in a new tab) - Hand tamperBudget price
Compacts gravel base in small areas and post holes. For a full slab base, rent a plate compactor.
See options on Amazon (opens in a new tab) - 4 ft levelMid-range price
Checks forms for level and slope, and plumbs block, brick and posts. A 4 ft level bridges small bumps that fool a short one.
See options on Amazon (opens in a new tab)
As an Amazon Associate we earn from qualifying purchases. Links to products are affiliate links — they cost you nothing extra and help keep these calculators free.
Frequently asked questions
How many bricks for a round fire pit?
For bricks laid flat and lengthwise around a 36 in ring, 3.1416 × 36 ÷ 7⅝ in is about 15 per course; with mortar joints, slightly fewer. Multiply by the number of courses — standard brick is only 2¼ in tall, so a 12 in wall takes about five courses.
What size should a fire pit be?
Inside diameters of about 36–48 in are common for backyard pits. Check local rules on size, setbacks and burn permits before you build.
Can I use cinder blocks for a fire pit?
Many people do, but ordinary concrete block isn’t made for direct fire and can crack or spall. A steel fire ring or a firebrick lining inside the blocks keeps the flames off them.
Sources
- Allan Block — How-to sheet #360, fire pit (opens in a new tab) — 28 AB York blocks per course make a ring about 81 in across.
- CMHA (formerly NCMA) CMU-TEC-001-23 — Concrete masonry unit shapes, sizes, properties and specifications (opens in a new tab) — Specified dimensions are 3/8 in less than nominal, so an 8×8×16 block is 7-5/8 × 7-5/8 × 15-5/8 in; nominal thicknesses 4–16 in; ±1/8 in tolerance.
- Brick Industry Association — Technical Note 10, Dimensioning and Estimating Brick Masonry (opens in a new tab) — Table 4: brick per 100 sq ft and mortar per 100 sq ft and per 1,000 brick for modular and non-modular sizes; add at least 5% to brick and 15–25% to mortar for waste.