Septic Tank Size Chart & Guide: How to Choose the Right Size
As a homeowner, it’s important to know the different septic tank sizes and what each one is capable of. Choosing the wrong septic tank size can lead to overflowing toilets, backed-up drains, contaminated groundwater, and expensive repairs. Moreover, your overall maintenance expenses would be higher due to more frequent and expensive septic tank pumping services.
This comprehensive guide will help you avoid those problems and choose the perfect septic tank gallon capacity for your onsite wastewater treatment needs, covering everything from basic sizing charts to the critical role of soil conditions. By the end, you should be fully equipped to make the best septic tank size selection for your home or business.
Local Septic Tank Regulations to be Aware Of
Before you install a septic tank, check with your state's environmental department and local city or county building office for approval. Different states have different requirements for the size and placement of the tank, as well as what materials can be used in its construction. Local regulations are the most important factor in septic tank sizing. They always override general guidelines.
For instance, the International Private Sewage Disposal Code gives general recommendations from the septic tank design to the number of manholes, inspection opening, sizing per dwelling unit, and so forth. Your local regulator and building codes come in handy since they specify the soil type as well as other local considerations.
Talking about soil type, this will affect how large the drain field needs to be, so be sure to have that professionally assessed before finalizing any installation plans.
Another thing to consider is if the septic tank is for residential or commercial use. Different regulations apply for each type. Lastly, the specific septic tank system already installed or that will be installed can also change the required septic tank size.
Before you even think about buying a septic tank, it´s ideal for you to contact your local health department or building authority. They will tell you the specific requirements for your area, including minimum tank sizes, setback distances, and whether two-compartment septic tanks are required.
Another thing to consider is if the septic tank is for residential or commercial use because there are usually different regulations for each type.
What Type of Septic System Will You Install?
While the terms "septic tank" and "septic system" are often used interchangeably, they aren't exactly the same thing. A septic tank is just one component of a complete septic system, which also includes a drain field and other components that work together to treat and dispose of wastewater. There are several types of septic systems, each designed to handle wastewater in different ways depending on factors like soil type, climate, and local regulations.
The type of septic system you choose can influence the required tank size. For example, systems designed for challenging soil conditions may require larger tanks or additional components.
The septic systems are listed below and can use polyethylene septic tanks if they require a tank.
- Conventional System
- Chamber System
- Drip Distribution System
- Aerobic Treatment System
- Mound Systems
- Recirculating Sand Filter System
- Evapotranspiration System
- Wetland Septic System
- Cluster Septic System
Some of these are known by other names, but the most common systems in use today are the conventional and chamber systems. The primary difference lies in how the drain fields are constructed. The conventional system uses gravel-filled trenches for drainage. The chamber system is gravel-less and uses some type of fabric-wrapped piping to distribute the liquid. Alternatively, you could use the well-known leaching chambers, which usually come in 2 different sizes (36 and 24” wide).
Here's a brief overview of how some of these septic systems relate to tank sizing:
- Conventional System: The standard septic system; tank sizing is based on factors outlined in this guide.
- Chamber System: Similar to conventional, but the gravel-less design can sometimes allow for a slightly smaller drain field (and potentially a smaller tank, depending on local regulations).
- Mound Systems: Often used in areas with high water tables or shallow soil. May require a larger tank and a pump chamber.
- Aerobic Treatment Systems: Provide more advanced treatment, potentially allowing for a smaller drain field (and, in some cases, a smaller tank).
- Sand Filter System: A septic tank is required as part of a sand filter system and is installed for the primary treatment of onsite wastewater.
How are Septic Tanks Constructed?
Before you decide on a septic tank size, familiarize yourself with the different materials of septic tanks. The most common type is concrete, but they require heavy-duty and expensive equipment for installation because they are so hefty. Fiberglass and plastic septic tanks are lighter in weight and can be placed in hard-to-reach or remote areas.
Comparing Concrete, Fiberglass, and Plastic Septic Systems
Variables That Affect the Size of the Septic Tank
A septic tank too small for a home will cause many problems, such as bad smells, flooding and blockages. The most common result of a septic tank that is too small is the water being released before it is purified. This means the solid waste in the septic tank won’t be broken down and will collect faster, which can cause overflows and blockages.
Is it possible to have a septic tank that's too big? If you're disregarding cost, then the answer is no. A correctly installed septic tank can never be too large — it can only be too small. In fact, most experts recommend going with a bigger size because it's often a safer and more preferred option. While a larger septic tank gallon capacity is more expensive, it will save you money in the long run as your family or home size increases. The pumping frequency would also be less. Ideally, you would need to pump your tank every 3-5 years due to the solid waste that bacteria can´t break down.
Note that the number of people living in your home is the primary factor in determining septic tank size. More people generally mean more wastewater.
Other Important Considerations in Septic Tank Sizing
- Water Usage: To find the most appropriate septic tank size for your home, you'll need to think about how much water you use daily. A septic tank's capacity determines how much waste it can hold before it needs to be pumped, which will impact the performance of your soil absorption field. As a rule of thumb, assume each person uses about 50-75 gallons of water per day. That translates to roughly 150-250 gallons per bedroom per day. This is a general estimate, and your actual usage may be higher or lower depending on your lifestyle and water-saving habits.
- Size of Your Home: While the size of your home is often considered a factor in selecting the proper size of a septic tank, the main issue is the number of bedrooms. That determines how many people will use the home, and average water usage is based on individuals living in the home. Notwithstanding, although the number of bedrooms can provide a rough estimate, it's less accurate than focusing on the actual number of people and their water usage habits. A large family living in a 2-bedroom home will likely need a larger tank than a single person living in a 3-bedroom home.
- Existing System: If there is an existing septic system on your property that will not be replaced with the new system, this will affect how big the new tank can be. Each system will require a specific amount of space for a drain field, and the projected water usage for the new system may limit the size of the tank.
Tips to Estimate Average Daily Wastewater Consumption
To get more accurate readings on the average wastewater produced in a day:
- Check your water bill: Your water bill will show your monthly water consumption, usually in gallons or cubic feet. Divide the total monthly usage by the number of days in the month to get your average daily usage. Notwithstanding, this isn’t the best metric to use as not all water goes down the drain. Consider uses like watering plants or filling a pool that doesn’t necessarily end up in a septic tank. That said, it’s a good start.
- Monitor your water meter: If you have a water meter, you can take readings at the beginning and end of a typical day to see how much water you use.
Consider any appliances that use a lot of water, such as dishwashers or washing machines. Each one will require additional capacity in your tank. Also consider other high-water usage items such as:
- Jacuzzi Bathtubs
- Hot Tubs
- Multi-head Showers
For each of these add-ons, we recommend adding an extra 250 Gallons per item.
Understanding Soil Conditions and Septic Systems
The type of soil on your property is a critical factor in the septic system design, and it directly impacts both the size of your drain field and, indirectly, the size of your septic tank.
Why does soil matter? The drain field (also called a leach field) is responsible for the final stage of wastewater treatment. It filters the effluent (liquid waste) from the septic tank before it re-enters the groundwater. Different soil types have different abilities to absorb and filter this effluent. Typically, leaching chambers are used in the drain field to allow for effluent percolation into the soil.
Here's a simplified overview of common soil types and their impact:
- Sandy Soil: Drains quickly. This can be good, but it may not provide enough time for proper treatment. May require a larger drain field (and potentially a larger tank) to compensate.
- Clay Soil: Drains very slowly. This can lead to backups and system failure if the drain field isn't designed correctly. May require a much larger drain field (and a larger tank) or an alternative system (like a mound system).
- Loamy Soil: A good balance of sand, silt, and clay. Generally ideal for septic systems.
- Rocky Soil: Can be challenging for installation and may require specialized drain field designs.
Percolation Test: To determine the drainage capacity of your soil, a percolation test (often called a "perc test") is required. This test measures how quickly water drains through the soil. A licensed professional (soil scientist, septic system engineer, or health department official) typically performs this test. The results of the perc test are essential for determining the proper size of your leach field, and this, in turn, influences the recommended septic tank size.
Always have your soil professionally assessed before installing a septic system. This is often a requirement of local regulations.
What Septic Tank Gallon Capacity Do I Need? Estimates Based on Water Usage
What Size Septic Tank Do I Need? Estimates Based on Bedrooms
Septic tanks come in different configurations, depending on the needs dictated by property size and geology. They include:
- Single-compartment tanks,
- Double-compartment tanks,
- Low-profile tanks and Standard tanks
- Above ground Holding tanks for jobsite and RV use.
The standard size of septic tank for residential properties will vary based on water usage and the size of the home. Here are some recommended septic sizes, depending on the number of bedrooms. Your specific situation may alter these.
It’s important to adjust the septic tank size for water-intensive appliances (e.g., washing machines), longer showers, or other factors that increase overall water usage.
How Big is a Septic Tank? Dimensions of Various Septic Tanks
These figures are based on low profile septic tanks:
- 750 gallon: 92 inches x 60 inches x 51 inches high.
- 1,000 gallon: 127 inches x 60 inches x 51 inches high.
- 1,250 gallon: 157 inches x 60 inches x 51 inches high.
- 1,500 gallon: 157 inches x 69 inches x 51 inches high
Additional Uses for Septic Tanks
While most people are not going to re-purpose a tank that has been collecting sewage, a new septic tank can be used for purposes other than storing wastewater, such as rainwater harvesting or stormwater collection. However, septic tanks aren’t approved for potable water use.
Tank Depot Specializes in Septic Tanks for Residential and Commercial Needs
Here at Tank Depot, we have septic tanks in various gallon capacities to fit any need, including pre-plumbed septic tanks and pump tanks. Our septic systems align seamlessly with conventional components such as leaching chambers and end caps for your drain/leach field.
Moreover, our high-density polyethylene septic tanks are durable and long-lasting, with ribs in the tanks for additional structure to withstand the surrounding soil pressure. As such, these tanks are perfect for residential, commercial and industrial applications.
Regardless of which septic tank size you need, be it for a small home or large business, Tank Depot has the septic tank that is right for you. Our experts can help you choose the perfect septic tank size for your specific needs, taking into account all the factors discussed in this guide, including local regulations and soil conditions. Contact us today for a free consultation and quote.