Septic Tank Sizing 

Some homes can’t connect to traditional sewer systems, so they rely on septic tanks instead. 

A septic tank provides reliable waste removal and helps prevent the risk of plumbing damage and groundwater contamination. There are multiple types of septic tanks available, and choosing the right one depends on a few factors:

  • House size and occupancy: The number of rooms in your house, as well as the number of people using its facilities, will help determine the best septic tank dimension for your needs. 
  • Water usage: Households that use large amounts of water with laundry machines, dishwashers, bathtubs, and more may need a more advanced system that can manage their daily output.
  • Budget: There are various types of tanks to choose from, each offering different advantages. If you have a limited budget, a less expensive tank made from a more lightweight material like plastic or fiberglass could be ideal.
  • Local regulations: Every town and municipality sets its own standards for septic systems, and these can influence the type of tank you can install or the material it must be made out of. You can find Boulders septic tank regulations in this document.

Before we delve into the details of septic tank sizes, let’s look at the different types available.

The Main Types of Septic Tanks

There are three types of septic tanks you can buy for a house: concrete, plastic or polyethylene, and fiberglass. 

Concrete is the most common material used in septic tanks, and it’s considered the gold standard thanks to its long lifespan. With proper maintenance, you can expect a concrete septic tank to last 30-40 years.

Plastic and polyethylene tanks are also durable, and they are more affordable, flexible, and lightweight than their concrete counterparts. Polyethylene is an extremely long-lasting type of plastic that is one of the most common materials in the world; it’s non-hazardous and great for a wide variety of uses, including creating a more budget-friendly septic tank.

Finally, we have fiberglass. Fiberglass septic tanks are reinforced with plastic and are easy to install. They’re stronger than plastic systems and naturally resistant to bacteria. 

All of these tanks can last 20-30 years, but if you’re really looking for the greatest long-term investment, a concrete tank is the best choice. However, many customers love the ease of installation and added benefits of plastic and fiberglass septic tanks.

Our team can help you make the right decision for your unique situation if you need more clarity on the pros and cons of each type of septic tank.

Now that we understand the different options available, we can take a closer look at septic tank systems and how to choose the right one for your home. 

There are also many styles of septic tanks to choose from: 

  1. Anaerobic System: This type of tank uses gravitational force and anaerobic bacteria to treat wastewater before moving it to a drain field. 
  2. Above-ground Septic System: When traditional in-ground systems aren’t an option or preferred, above-ground tanks can work instead. The tank and drain field will be located above ground, so many homeowners also invest in landscaping to avoid eyesores on their property. 
  3. Aerobic Septic System: The aerobic system uses oxygen to promote the growth of aerobic bacteria, which break down waste faster than anaerobic bacteria. 
  4. Mound System: Mound septic systems are a type of above ground septic tanks that direct wastewater to a drain field in a sand mound above natural soil.
  5. Pressure System: A pressurized pump moves wastewater to the drain field. Its motorized process helps ensure efficiency. 
  6. Recirculating Sand or Gravel Filter Septic System: Waste is moved through a sand or gravel filter repeatedly before being dispersed to the drain field. In some cases, the water can be reused for irrigation. 
  7. Bottomless Sand Filter Septic System: This type of system relies entirely on sand to treat wastewater; low pressure is applied to remove pollutants as the water passes through the sand. Although efficient, these systems have high maintenance costs.

Choosing the right system will vary depending on your needs and budget. 

It’s important to consider more than just initial costs; every septic tank requires routine cleaning and maintenance to operate at its best. More advanced systems will cost more, so you should carefully consider the total cost of ownership before settling on any particular system. 

We know this is an extensive process and are here to help. Our professional team will work with you every step of the way to compare and contrast systems until you find the perfect one for your needs.

Septic Tank Sizes

How much should a septic tank be for a house? 

In Boulder, CO the minimum septic tank sizes are as follows:

2 or 3 bedrooms – 1,000 gallons

4 bedrooms – 1,500 gallons

Each additional bedroom +250 gallons

Now, these are just the minimum requirements. The size of your septic tank will also depend on the number of people living in the house and their water usage.

Septic Tank Dimension

A septic tank for a house will average 4.5 feet wide, 8 feet long, and 6 feet tall. 

These dimensions will change if you live in a larger home (over 2,500 square feet). Generally, adding more gallons to homes larger than this size can ensure greater performance and reliability. 

Septic Tank Capacity 

A tank’s capacity is the amount of wastewater it can handle. Larger homes with heavier water usage will naturally need a system that has a greater capacity. 

There are residential septic tanks that can accommodate up to 3,500 gallons, so even large properties can find the right fit for their needs. 

It’s important to work with a skilled professional who understands how to determine the appropriate size of a septic system for your home. They will do this by looking at the number of bedrooms in your house, its total square footage, and your daily water usage.

Septic Tank Shape

Septic tanks come in two shapes: cylindrical and rectangular. The latter is the most common and easiest to install. Plastic or polyethylene tanks tend to be cylindrical to ensure better weight distribution. 

Both sizes are acceptable and perform their job well; when it comes to getting the best tank for your home, one of our professionals can determine what shape would be ideal given the material you prefer and the size of your home. 

What Size Septic System Do I Need?

The right septic tank for your home will depend on how much water you use and the square footage of your house. More bedrooms generally mean more people, which requires a larger septic tank to accommodate their needs. 

The more wastewater a home generates, the larger its septic tank should be. 

How to Calculate Septic Tank Size

There are two factors you should consider when calculating septic tank size: 

  1. Estimated daily water usage: Most people use around 70-100 gallons of water per day. Multiply these figures by the number of people in your household. This will give you a good starting range for what size septic tank you should buy. 
  2. Consider the number of bedrooms: The general industry rule is that a septic tank should account for at least two people per bedroom. 

Recommended Septic Tank Size

While the sizes vary for homes by square footage and water usage, some municipalities set a minimum gallon requirement for septic tanks. Be sure to check your local regulations and keep this in mind while exploring your options. The typical minimum septic tank requirement is 1,000 gallons. 

Septic Tank Size for a 2-Bedroom House

A two-bedroom home requires a 1000-gallon septic tank, provided they do not have extraordinary water usage. 

Septic Tank Size for a 3-Bedroom House

Three-bedroom homes can benefit from a starting septic tank capacity of 1,000 gallons. This could increase to 2,000 in cases with heavy water usage. 

Septic Tank Size for a 4-Bedroom House

A four-bedroom house can benefit from a septic tank that holds 1,500 gallons to 2,500 gallons of wastewater. 

Septic Tank Size for a 5-Bedroom House

Homes with five bedrooms will likely need a septic tank with 1750+ gallons.

Number of BedroomsRecommended Septic Tank Size (by Capacity)Average Square Footage of Home
1 bedrooms1,000 to 1,500 gallons700 to 1,500 square feet
2-3 bedrooms1,000 to 2,000 gallons1,500 to 2,200 square feet
4 bedrooms1,500 to 2,500 gallons2,200 to 3,000 square feet
5 bedrooms1750 to 3,000 gallons3,000 to 3,500 square feet

Keep in mind that local building codes and regulations will influence septic tank size requirements. It’s also important to factor in water usage and wastewater produced to know precisely which size septic tank is perfect for your home.

Please contact us to learn more about septic tank installation in Boulder, CO. Our contractors will be happy to help you determine the perfect size and type of tank for your home.

In business for over 10 years, Mountain Contractors, LLC has deep experience in the septic and sewer industry. They’ve successfully and professionally provided sewer and septic services to Boulder and Gilpin Counties and have excellent online feedback and reviews. For help with all your home sewer, water, and septic tank needs, call Mountain Contracting LLC today.