Quick Answer
The number of blocks needed to build a fire pit depends on the size and design. A basic 3-foot diameter fire pit would require around 60-100 blocks. Larger fire pits may require 150-300 blocks. Custom designs with multiple levels, benches, etc. will require more blocks. The key factors determining block quantity are the fire pit’s diameter, wall height, and complexity of the design.
How Many Blocks for Common Fire Pit Sizes
| Fire Pit Diameter | Estimated Blocks Needed |
|---|---|
| 3 feet | 60-100 |
| 4 feet | 100-150 |
| 5 feet | 150-200 |
| 6 feet | 200-300 |
For a basic single-walled fire pit, the table above gives estimates for common sizes. The actual amount can vary based on the wall height and thickness. Standard wall height is around 1-2 feet. You may need up to 50 more blocks if building a taller wall.
The estimates are for fire pits made from solid concrete blocks (8″ x 8″ x 16″) or similar sized landscaping blocks. Different materials like brick, stone, or pavers will require different block counts.
Design Factors That Increase Block Count
While the table above covers simple circular designs, certain elements will require more blocks:
Multi-Tiered Walls
Fire pits with a shorter inner wall and taller outer wall (2-tiered) need extra blocks for the second wall. Each tier added generally requires 50-100 more blocks.
Curved or Octagonal Designs
Fire pits with a rounded or octagonal shape need about 10-20% more blocks than a simple circle. The curved sides use more material than straight lines.
Seating Walls, benches and other features
Fire pits that incorporate built-in seating, corner benches, planting ledges, or other decor features will require additional blocks. Count each linear foot of seating wall at 8-12 blocks.
Thicker Walls
Increasing wall thickness from 1 block (8 inches) to 2 blocks (16 inches) doubles the blocks needed. Thicker walls improve insulation for more heat retention.
Retaining Walls
If building a sunken or elevated fire pit, retaining walls to hold back soil also consume blocks. Estimate retainment needs separately from fire pit sizing.
Veneer or Masonry Facing
Natural stone, brick, or other veneers add beauty but also blocks over a supporting wall. For each square foot of veneer, estimate 12 bricks or 4-6 stones.
Estimating Charts by Fire Pit Size
These charts provide block estimates for common fire pit sizes and designs:
Basic 3 Foot Fire Pit
| Feature | Blocks Needed |
|---|---|
| Circular wall – 1 ft high x 1 block thick | 60-70 |
| Circular wall – 2 ft high x 1 block thick | 80-100 |
| Circular wall – 2 ft high x 2 blocks thick | 140-160 |
Basic 4 Foot Fire Pit
| Feature | Blocks Needed |
|---|---|
| Circular wall – 1 ft high x 1 block thick | 100-120 |
| Circular wall – 2 ft high x 1 block thick | 130-150 |
| Circular wall – 2 ft high x 2 blocks thick | 220-260 |
Basic 5 Foot Fire Pit
| Feature | Blocks Needed |
|---|---|
| Circular wall – 1 ft high x 1 block thick | 140-170 |
| Circular wall – 2 ft high x 1 block thick | 180-220 |
| Circular wall – 2 ft high x 2 blocks thick | 300-360 |
The charts illustrate how the block count increases significantly with greater diameter, height, and thickness. These estimates are for the fire pit alone – any additional patio, retaining walls, etc. require extra blocks.
Block Options for Fire Pits
Concrete Blocks
Standard 8″ x 8″ x 16″ solid concrete blocks are commonly used. They provide good stability and heat resistance. For a textured look, split-face blocks are a nice choice.
Landscape Blocks
Blocks designed for landscaping and retaining walls can also work. Look for steel-reinforced blocks rated for fire pits. The lip and notch patterns add decorative appeal.
Fire Brick
Brick made specifically for fireplaces and wood stoves can withstand high heat. They are more expensive than typical masonry brick. Fire brick is best used as a liner rather than the main structure.
Retaining Wall Blocks
Smaller blocks for short retaining walls, like Allan Blocks, are not ideal for the main fire pit structure. Use larger blocks as the base and retainers as accents.
Natural Stone
Granite, limestone, and other natural stones add beauty when used as a veneer over a concrete block wall. Not all stone is heat-safe – do research before selecting stone.
How to Calculate Needed Blocks
To estimate your block needs, follow these steps:
1. Measure the fire pit diameter and design shape (circle, square, etc).
2. Decide on wall height and thickness (in blocks, 1 block = 8 inches typically).
3. Calculate the circumference by measuring the diameter and multiplying by pi (3.14).
4. For the wall length, multiply the circumference by the wall height in blocks.
5. For the total blocks, multiply the wall length by the thickness in blocks.
6. Add extra for any special features – multi-tiered walls, benches, etc.
7. Order 10-20% more than the estimate to be safe.
Here is an example calculation:
Fire Pit Diameter: 5 feet
Wall Height: 2 feet (2 blocks high)
Wall Thickness: 1 block thick
Circumference = 5 feet x 3.14 = 15.7 feet
Wall Length = 15.7 feet x 2 blocks high = 31.4 feet
Wall Length x Thickness = 31.4 feet x 1 block thick = 120 blocks
For a basic 5 foot diameter fire pit with a 2 foot high, single block wall, you would need around 120 blocks. Add more for any decorative features or thicker walls.
Tips for Building Your Fire Pit
Here are some key tips to help build your fire pit with blocks:
– Dig out the area at least 6 inches deep and make sure soil is compacted.
– Use a gravel base topped with sand for drainage.
– Start by dry stacking the first course of blocks to layout the shape.
– Use construction adhesive between block layers for strength.
– Stagger vertical joints for stability and interlock blocks when possible.
– Install tie rods anchored in concrete for reinforced walls over 2 feet high.
– Slope the fire pit floor slightly toward the center to allow rain drainage.
– Use high-temperature concrete or mortar rated for fire pits.
– Cure the concrete completely before building a fire – at least 72 hours.
– Include openings at the base for airflow if enclosing the bottom.
Conclusion
When planning a DIY fire pit, determining the required block quantity is an important first step. While the project may initially seem daunting, breaking it down into sizes and features helps generate a realistic block estimate. Typical fire pits need anywhere from 60 to 300+ solid concrete blocks, depending on the overall diameter and design elements. With careful planning, the right materials, and a methodical approach, you can create a beautiful and long-lasting fire pit using blocks as the building foundation.
