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How Big of a Septic Tank Do I Need? Factors & Size Chart

Big plastic septic tanks system

If you’re looking for a septic tank size chart, you’ve come to the right place! Figuring out how big of a septic tank you need can be confusing because so many factors are involved! But don’t worry. We’ve got your back.

We’ll try to make this as easy as possible for you. So, without further ado, let’s dive into our guide to help you determine the right size septic tank for your needs. And be sure to stick around for our handy septic tank sizing chart!

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Sizing Your Septic Tank

The first step for figuring out what size septic tank you need is to determine how many people live in your house. The number of bedrooms (or bathrooms) in your home isn’t as important as the number of people who live there. Generally, one person needs a minimum of 750 gallons of tank capacity.

Not surprisingly, that’s the smallest tank size you can buy. However, it’s worth pointing out that some residential areas require a bare minimum of 1,000 gallons.

Next, you need to think about how much wastewater your family produces daily. The more people in the home and the more water-intensive activities they do (like long showers, multiple loads of laundry, etc.), the bigger your tank needs to be.

As a rule of thumb, assume each person uses about 100 gallons of water per day. Multiply this amount by the number of people in your household, and you can calculate how much wastewater needs to be accommodated by your tank.

Finally, consider any appliances that use a lot of water, such as dishwashers or washing machines. Each one will require additional capacity in your tank.

fiberglass septic tank
Photo By: kaninw, Shutterstock

Septic Tank Sizing Chart

Now that you have an idea of the factors to consider when sizing your septic tank, here’s a helpful chart outlining the approximate size tanks for different scenarios. It’s important to keep in mind that this chart is only meant as a guide—every situation will be different, and you should always consult with an expert before making a final decision.

Number of People in Household Tank Size (Gallons)


1–2 people


750–900 gallons
3 people


1,000–1,200 gallons
4 or more people


1,250–2,250 gallons

We hope this septic tank sizing guide was helpful! Now that you know how to size your septic tank, you should have a much easier time finding the perfect one for your needs.

How Do I Know What Size Septic Tank I Need?

Another method you can use is to go by how many bedrooms are in your home. The same figures apply as above, only replacing people with bedrooms. So, a one-bedroom house, for example, would require a 750-gallon septic tank, and so on.

If you’re ever in doubt, don’t panic. Simply call a qualified and reliable plumber to walk you through it. They should be able to tell you exactly what you need for your household size.

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Tired of using chemical-laden store cleaners to deodorize your drains? Switch to hydrogen peroxide for a safe, natural, and highly effective alternative that will keep your pipes and drains smelling great.

Featured Image Credit: Artem Bruk, Shutterstock


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