Building a fire pit in your backyard can be a fun DIY project that allows you to enjoy the ambiance and warmth of an outdoor fire. One of the key steps in constructing a fire pit is determining how many bricks you will need. The number of bricks required depends on the size and design of the fire pit.
How big should your fire pit be?
When deciding on the size of your fire pit, first consider how you plan to use it. Will it be mainly for roasting marshmallows or cooking over the fire? Or do you want a larger pit for a bigger fire to gather around in the evenings? Here are some typical fire pit sizes to consider:
- Small – 3 feet diameter – great for roasting marshmallows
- Medium – 4-5 feet diameter – good for cooking over
- Large – 6+ feet diameter – ideal for larger gatherings and ample seating
In general, a smaller fire pit will require fewer bricks, while a larger diameter fire pit will need more bricks. You also need to decide if you want a round or square/rectangular shape. Square pits generally require a few more bricks than a round design.
How many bricks do you need for a round fire pit?
If building a round fire pit, the number of bricks needed can be estimated using the following formula:
Number of bricks = (Pi x (fire pit diameter / 2)2) / (brick length x brick height)
For example, let’s assume you want a 4 foot diameter fire pit and are using standard 9 x 4.5 inch bricks:
(3.14 x (4 ft / 2)2) / (9 in x 4.5 in) = 28 bricks
So you would need approximately 28 bricks for a 4 foot round fire pit.
This formula accounts for the curved shape of the round fire pit. The key measurements needed are the fire pit diameter, brick length and brick height. Apply those measurements to the formula to determine the estimated number of bricks.
How many bricks for a square or rectangular fire pit?
For a square or rectangular fire pit, the calculation is a bit simpler. You first need to determine the total area of fire pit by multiplying length x width. Then divide the area by the area of a single brick to get the estimated number of bricks.
For example, if building a 4 x 4 foot square fire pit using 9 x 4.5 inch bricks:
- Fire pit area: 4 ft x 4 ft = 16 sq ft
- Brick area: 9 in x 4.5 in = 40.5 sq in = 0.28 sq ft (converting to square feet)
- Fire pit area (16 sq ft) / Brick area (0.28 sq ft) = 57 bricks
So for a 4×4 foot square fire pit, you would need approximately 57 bricks.
The same formula would apply for a rectangular design – simply substitute the length and width measurements into the area calculation.
How much mortar or concrete do you need?
In addition to bricks, you will also need mortar or concrete to lay the fire pit bricks. For mortar joints around 1/2 inch thick, here is a rough estimate:
- 1 bag of mortar covers 8-10 square feet
- 1 yard of concrete covers 80-100 bricks
So continuing the example above with a 4 foot round fire pit and 28 bricks:
- Fire pit area: 4 ft diameter = 12.6 sq ft
- With 1/2 inch mortar joints, estimate needing 2 bags mortar (16-20 sq ft coverage)
And for the 4×4 square fire pit with 57 bricks:
- With 1 yard concrete (covers 80-100 bricks), you would need 1 yard
These are rough estimates but help give an approximation of mortar needs. Having extra mortar or concrete is ok for ease of application.
How high should you build the fire pit walls?
A typical fire pit wall height is around 12-16 inches above ground level. However, consider these factors when determining your wall height:
- Seating – If using built-in seating around the pit, account for the seat height in the wall elevation.
- Safety – To prevent accidental falls, higher walls are safer for pets and young children.
- Fire visibility – Lower walls allow the fire to be more visible.
- Fire containment – Higher walls contain more heat and embers.
Also check your local building codes, which may specify a certain fire pit wall height. Once you decide on the height, you can calculate the number of courses, or rows, of bricks needed.
How many courses of bricks?
Standard brick heights are 2 1/4 inches for bricks and 3 1/2 inches for pavers. To determine the number of courses needed:
Number of courses = Wall height / Brick height
For example, for a 12 inch wall height using standard 2 1/4 inch high bricks:
Number of courses = 12 in / 2.25 in = 5 courses
If using 3 1/2 inch high pavers, that same 12 inch wall would be:
Number of courses = 12 in / 3.5 in = 3 courses
Always round up to the nearest full course. It’s better to have a few extra bricks than to come up short.
What material to use for the fire pit base?
The bottom of the pit should be a non-combustible material like dirt, sand, crushed rock or gravel. Avoid materials like wood, grass or mulch which can burn.
For drainage, put down a 5+ inch layer of crushed rock, gravel or sand. On top of that, add a 1 inch layer of sand or fire brick/fire glass for aesthetics.
Avoid river rocks around the fire as they may explode from heat exposure. Use larger boulders or fire rated rocks around the outside instead.
Do you need fire brick or refractory mortar?
Fire bricks and refractory mortar are not strictly required but are good for heat resistance:
- Fire brick – Resists heat and flames better than typical clay bricks
- Refractory mortar – Withstands heat up to over 2000°F. Regular mortar may crack under high heat.
These specialized masonry materials provide added protection but tend to be more expensive. For a backyard DIY fire pit, regular clay bricks and mortar are usually sufficient unless you plan extremely large, hot fires.
What tools do you need to build a fire pit?
Having the right tools will make constructing a brick fire pit much easier. Recommended tools include:
- Shovel – For excavating and preparing the fire pit foundation
- Level – To ensure level ground and properly stacked courses
- Trowel – For mixing and spreading mortar or concrete
- Gloves – For handling bricks and materials
- Hand tamper – For compacting mortar and leveling bricks
- Brick hammer – Optional, for splitting bricks if needed to fit
- Measuring tape – For measuring pit dimensions and mortar joints
- Broom – For finishing and smoothing mortar joints
A wheelbarrow, mixing tools like a hoe, and a spade for digging can also be helpful. Safety gear like goggles, boots, and gloves is recommended.
Tips for laying bricks
Follow these tips for properly laying the bricks:
- Start by dry laying the bricks in the pattern you want. This allows you to visualize the layout and make adjustments.
- Use excavated dirt or sand underneath for a level base. Compact it thoroughly before starting.
- Spread a 1/2 inch thick layer of mortar with the trowel. Firmly press the bricks into the mortar bed.
- Check level and alignment every few courses using the level tool.
- Let the mortar dry partially between courses. Fully cured mortar takes 28 days.
- Tool the joints after several minutes for a concave profile to help protect the mortar.
- Stagger vertical joints from course to course for better bonding.
Take your time laying the bricks and let the mortar fully cure before building your first fire. This helps prevent cracks or dislodged bricks.
What kind of base is needed under the bricks?
A proper base underneath the fire pit bricks helps prevent sinking or cracking. Options for bases include:
- Gravel base – 4-6 inches of compacted gravel creates excellent drainage.
- Concrete base – Poured slab or pavers provides a sturdy foundation.
- Sand base – Compacted sand base of 4+ inches.
- Dirt – Compacted subgrade soil can work but may erode over time.
Gravel, concrete, or sand bases are preferred for stability. The base should extend at least 6 inches wider than the fire pit diameter.
How can you decorate or finish a brick fire pit?
Adding finishing details can really enhance the look of your DIY brick fire pit. Decoration possibilities include:
- Capstones or coping – Top off the wall with large pavers or cut stone.
- Steel ring insert – Contain the fire in a steel ring for safety and style.
- Fire glass – Blue or green glass pieces reflect the flames beautifully.
- Rocks or boulders – Place natural stone around the exterior.
- Stucco or plaster – Coat the bricks for a smooth, contemporary look.
- Engraved or patterned bricks – Alternate brick designs for visual interest.
Get creative with multiple colors and textures of brick or stone. Just be sure to select fire-rated materials placed a safe distance from the flames.
Key takeaways
Here are some key tips to remember when calculating how many bricks you need for a DIY fire pit project:
- Determine the fire pit diameter or dimensions based on intended use and yard space.
- Use pi x radius squared for round pits or length x width for square/rectangular pits to get the area.
- Divide the fire pit area by the brick area to estimate number of bricks needed.
- Factor in wall height, brick dimensions, and mortar joints to calculate courses.
- Prepare a gravel, concrete or compacted sand base extending 6+ inches past the outer edges.
- Have extra bricks, mortar and tools available to make progress easier.
- Follow safety measures and check local building codes for fire pit regulations.
With some planning and these brick calculations, you can create the perfect backyard fire pit design to enjoy for years to come.
Conclusion
Determining the number of bricks required for a DIY fire pit involves calculations based on the desired shape, size, wall height and materials. Measure the fire pit diameter or dimensions, allow for mortar joints, and divide by the size of bricks being used. A rough materials estimate is 1 yard of concrete or 2 bags of mortar per 100 bricks. Have extra bricks on hand and build on a gravel, concrete or compacted sand base extending past the edges. Follow safety guidelines and enhance with decorative touches. With the right planning and preparations, a backyard fire pit makes a wonderful addition for relaxing evenings around the fire.
