We’re thinking about getting a fire pit in our backyard, but we wanted to know exactly what size we need to provide the proper amount of heat. The only problem is, we weren’t able to find a good answer. So, I did some more research. Here’s the best way to calculate the size of the fire pit you need.
The average wood fire pit is 36-44 inches in diameter while the average gas fire pit is 22 inches in diameter. When calculating your fire pit size, first find out how many people your fire pit needs to heat. 2-3 people should have a small fire pit, 4-6 people a medium fire pit, and 6 or more people a large fire pit.
Let’s take a look at exactly how to calculate your fire pit’s size, dimensions, and other metrics.
How to Calculate Fire Pit Size
|Wood Fire Pit Size||Round (Diameter)||Square (Length & Width)|
|Small (2-3 People)||30-36 inches||27-32 inches|
|Medium (4-6 People)||36-44 inches||32-39 inches|
|Large (6+ People)||44-60 inches||32-53 inches|
The biggest factor when deciding on a fire pit is to find out how many people it needs to heat. After all, you don’t want to waste space in your backyard or burn excess fuel unless it’s necessary.
Once you determine the number of people you need to keep warm, match it with the fire pit size and the average dimensions listed in the table above. This should give you a solid, rough estimate of the fire pit size you need.
Side note: if you’d like to determine the other measurements for your fire pit, including circumference, radius, and area, use this helpful circle calculator. You only need to enter 1 value, such as diameter, to get the rest of the dimensions.
For example, if the diameter of your fire pit is 36 inches, and you’d like to convert it to a square fire pit, find the total area of the circle using that calculator (1018 inches) and then square root it (32 inches).
If you’re not a fan of the circle calculator above, I liked this square in circle calculator.
Average Fire Pit Dimensions
The average round fire pit has an inside diameter of 36-44 inches for wood and 22 inches for gas. Square fire pits have an average inside length and width of 32-39 inches for wood and 20 inches for gas. In any case, allow for an additional width of 12-20 inches for the outside wall.
Fire pits aren’t that efficient when they’re too small, so try not to go below 30 inches in inside diameter. This is because some space is required for proper airflow to feed the wood fire.
On the other hand, wood fire pits over 60 inches in inside diameter are generally too large and burn too much fuel. The increased airflow burns the fuel faster and spreads the heat over too wide of an area. Larger fire pits can also be difficult to talk over since the distance between people is greater.
Some say fire pits can be up to 6 feet in diameter, but I recommend no more than 5 feet. The same goes for length and width.
Recommended: Are Backyard Fire Pits Legal? Here’s How To Find Out
How Tall or Deep Should Fire Pits Be?
Above-ground fire pits should ideally have walls 18 inches tall. The minimum and maximum height for fire pit walls are 12-20 inches. Fire pits that are too low will make people squat or bend over while those that are too tall block the fire pit’s heat. In-ground fire pits should have a depth of 18 inches.
Wood vs Gas Fire Pits
|Size||Wood Fire Pit||Gas Fire Pit|
|Small||10,000-25,000 BTUs||10,000-20,000 BTUs|
|Medium||25,000-60,000 BTUs||20,000-30,000 BTUs|
|Large||60,000-100,000+ BTUs||30,000-70,000 BTUs|
For comparison, the average fireplace heats about 30,000 BTUs or about 1,500 sq. ft. of space. This is for indoor spaces which are fairly insulated, so there will be much more heat loss outdoors.
Wood fire pits get anywhere from 10,000 to 100,000 BTUs and up, depending on the wood type, wood dryness, wind, outdoor temperature, the structure of the fire pit, and other factors.
The heat radius of wood fire pits is generally around 3-10 feet. Choose a wood fire pit if you’re looking for maximum heat output.
Gas fire pits often output around 10,000 to 30,000 BTUs, with some models going up to 70,000 BTUs. It’s difficult to find models that go higher than that due to manufacturer restrictions and safety.
Gas fire pits most commonly run on propane, but some use natural gas.
Similar to wood fire pits, much of the heat from gas fire pits is lost as it travels upwards. This means an immediate heat loss of about 40%. For this reason, many gas patio heaters have a lid that reflects heat downward.
The heat radius of gas fire pits ranges from 2-10 feet. Again, this depends on the weather, flame size, and other factors. For best results, opt for one with higher BTUs and a medium that retains a lot of heat such as steel, brass, concrete, or ceramic balls.
Keep in mind that variables such as wind, outdoor temperature, and the build of the fire pit contribute to how much heat it provides. Since heat travels up, it’s important to have a fire pit that retains heat and radiates it outward.
Round vs Square Fire Pits
Once you choose which type of fire pit you want, consider if you’d like a rounded fire pit or a square one.
Square fire pits are not only easier to measure and build, but they’re more efficient in terms of space and seating. However, round fire pits are typically more visually appealing. Both styles of fire pit should have their interior lined with a steel ring.
Other than that, there’s not too much of a difference. It mostly comes down to preference.
How Many Blocks Do Fire Pits Need?
When building a round fire pit, most people use trapezoidal blocks, which are narrowed on one side. This allows the blocks to fit cleanly together in a circle. You’ll need around 42-54 of them or 14-18 per course. If you’re using bricks instead, aim for about 80 bricks.
More Tips for Fire Pits
- Check burn bans before building or buying a wood fire pit. I check this by Googling “burn ban” along with typing in my county. Your county’s website should come up with a message if there’s an active burn ban or not.
- Wood fire pits repel bugs, but gas fire pits don’t. To learn more about if certain fire pits can repel bugs or not, check out my other post: Do Fire Pits Repel Bugs & Mosquitos?
- Check with your county and building codes for proper safety and clearance of fire pits. Typically, this is no less than 20 feet from houses, fences, structures, tree limbs, and other objects.
- Keep chairs and other flammable objects at least 30 inches from the fire.
- Before installing permanent seats such as a seating wall, test the fire pit at full heat with mobile chairs. Move the chairs to your preferred distance and measure it.
- Select hardwoods with under 20% moisture content for the best wood fire. Typically, these logs need to season (dry) for at least a year. Check out my other post for tips to keep a fire pit going.
- A fire pit sitting wall needs to be 24-30 inches away from the fire pit to allow people to put their feet up by the fire. It also provides them enough space to walk around the fire pit.
- Line your fire pit wall with a steel ring to better contain the fire and protect your bricks.
- When wind speeds exceed 15 miles per hour fire pits lose much of their heat. This also poses a problem with embers blowing around.
- You should know that fire pits aren’t an efficient way to heat
- Keep a hose with the water on, a fire extinguisher, and sand nearby
- Hire an expert or a contractor if you aren’t sure what size of fire pit you need. They’ll be able to gauge the proper sizing, dimensions, type, and location for your fire pit.
To see how to build a great fire pit on a budget, check out this video by Fix This Build That.
Need More Help?
You can always ask us here at Fireplace Tips, but you should know the other resources available to you! Here are the resources we recommend.
- Chimney Safety Institute of North America (CSIA): The CSIA is your BEST resource for fireplace and chimney safety at home. They’re a non-profit governed by a volunteer board of directors dedicated to the education, training, and certification of chimney and industry related professionals.
- Self-Sufficiency and Off-Grid: If you’re like me and passionate about off-grid and self-sufficiency, see my number 1 resource—Abundance Plus. Check out their Frugal Homesteading Course on growing 90% of your own food. Get 7-days free and 10% off with the code: TYLER10