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Calculating the septic tank size is something every septic system owner should know so you can plan for how often it needs to be pumped to keep it operating at its peak. Even a minimal amount of preventative maintenance costs much less than the cost of a new system. Therefore, it is important to know when your septic tank will need pumped so you do not miss a maintenance service. Failure to pump your septic tank regularly will result in solids or grease overflowing into your drainfield. If the buildup of solids in the tank becomes too high and solids move to the drainfield, this could clog and strain the system to the point where a new drainfield will be needed.

So before it is too late, find out the size of your septic tank.


Types of Septic Tanks

There are three common types of septic tanks used in residential construction.

  • Concrete septic tanks
  • Polyethylene/plastic septic tanks
  • Fiberglass septic tanks

Concrete septic tanks are the most common, but because of their weight require heavy machinery to install. Polyethylene and fiberglass are much lighter, one-piece units. This makes them ideal for remote, hard to reach places. Before purchasing a septic tank system, check with your local building department for codes and regulations regarding onsite wastewater treatment.


Why Choosing the Right Septic Tank Size Matters

If an undersized septic tank exceeds its holding capacity, sewage can back up into your home, so when you are putting in a septic tank, it is essential that you take the time to calculate the correct size. Most municipalities require even the smallest septic tanks to hold approximately 1,000 gallons. The required capacity increases from there based on the number of bedrooms, occupants, bathrooms and fixtures the septic system will service.


How Much Water Do You Use?

There are a number of methods of calculations to determine the septic tank size that is needed for your home. The most accurate and reliable way is with water usage. The size of the septic tank required is based on the amount of water it will handle and in turn will be dispersed into the field lines. It should be noted that in many parts of the country, the minimum size tank allowed is 1,000 gallons.

Regular Use: 50-100 gallons per person per day

Bathing: 25-60 gallons per bath/ shower

Dishwasher: 7-50 gallons per load (check your manual)

Garbage Disposal: 4-6 gallons per day

There are other things, such as pools, water softeners, and lawn irrigation that are not included here. Try to keep these in mind as you work out your estimate. In homes with low water usage, your reservoir will need to hold roughly twice the number of gallons you use. As your water usage goes up, the gap narrows some.


Calculations by House Size

A less accurate guide to calculating your tank size is the number of bedrooms in your home or the square footage of the home. For a 1,000 gallon septic tank, how many bedrooms can you have? It is difficult to say because of varying water usage based on your situation. These calculations assume all bedrooms will be occupied and base the estimated water usage on this data. If you live alone in a three bedroom house, these calculations will be off. The reasoning for using these calculations is that a new owner may occupy all the bedrooms and the tank must be of an adequate size to handle the load.

Listed here are the recommended tank sizes based on number of bedrooms.

  • One or two bedrooms under 1,500 square feet: 750 gallon tank
  • Three bedrooms under 2,500 square feet: 1,000 gallon tank
  • Four bedrooms under 3,500 square feet: 1,200 gallon tank
  • Five or six bedrooms under 5,500 square feet: 1,500 gallon tank


Septic Tank Size Affects Pumping Schedule

The size of your septic tank matters because that affects how often it needs to be pumped to keep operating at its peak. Generally, we recommend pumping your septic tank every 3-5 years — the smaller the tank, the more often it must be pumped. Tanks that go too long without this maintenance are likely to become backed up or fail, requiring expensive repairs or replacement.


Planning Your Drainfield

Here are some valuable tips for planning the location of your drainfield.

  • Do not allow vehicles on or around the drainfield.
  • Do not plant trees or anything else with deep roots near the bed of the drain field as roots often clog the pipes.
  • Do not drain downspouts or sump pumps into the septic system.
  • Do not tamper with or alter with natural drainage features without researching and considering how it will affect the drain field.
  • Do not build additions over the drain field or cover it with concrete, asphalt, etc.
  • Make your septic tank cover as accessible as possible to allow for easy maintenance and inspection.
  • Plant grass to assist with evaporation and prevent erosion.


Get Help Choosing the Right Septic Tank Size

These numbers only serve as a general guideline, and the functionality of your entire system depends on you getting your numbers right. Don’t leave it to chance. Call West Coast Sanitation. Our experts know that you don’t have time to deal with septic problems. If you think that your system has reached capacity, please give us a call right away. We have professionals ready to answer your questions and get your system working properly again.