Septic Tank Size Calculator

This septic tank size calculator is a simple tool designed to help homeowners and builders determine the minimum size of a septic tank required based on the number of bedrooms in a residential property. It’s Free , easy to use and there’s no sign up required.

Septic Tank Calculator

Enter the number of rooms to calculate your septic tank size

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How the Septic Tank Size Calculator Works:

The calculator works by first determining the number of people expected to reside in the property based on the number of bedrooms. It uses a standard occupancy rate, where one bedroom is assumed to have three occupants, two bedrooms have four occupants, three bedrooms have 5 occupants, and so on.

Once the number of occupants is determined, the calculator applies a simple formula to calculate the minimum size of the septic tank required. The formula used is:

Minimum Size of Septic Tank = (Number of people x 150 L) + 2000 Liters

This formula is based on the assumption that each person generates approximately 150 liters of waste per day, and a minimum capacity of 2000 liters is required to comply with building regulations and environmental agency general binding rules.

septic tank size calculator

How the Results Were Arrived At:

The results provided by the septic tank size calculator are derived from the standard guidelines and regulations set by building authorities and environmental agencies. These guidelines take into account factors such as the number of occupants, average daily waste generation per person, and the minimum capacity required for proper waste treatment and disposal.

The formula used in the calculator is a simplified version of the more complex calculations used by professionals in the field, but it provides a reasonable estimate for residential properties with up to 10 bedrooms.


  1. How accurate are the results generated by the septic tank size calculator ? The result generated by this calculator is accurate.The calculator takes into consideration the appropriate guidelines set by the building authorities.
  2. Why is there a minimum size of 2000 liters for the septic tank? The minimum size of 2000 liters is a general guideline set by building regulations and environmental agencies to ensure that the septic tank has sufficient capacity for proper waste treatment and disposal, even for smaller households.
  3. Can I use a smaller septic tank than the recommended size? It is not recommended to use a smaller septic tank than the calculated size, as it may lead to overflow or improper waste treatment, which can cause environmental and health issues.
  4. Does the calculator account for additional water usage, such as from a washing machine or dishwasher? No, the calculator does not account for additional water usage from appliances or other sources. It is based solely on the estimated waste generation per person.
  5. Can I use this calculator for commercial or industrial properties? No, this calculator is designed specifically for residential properties with up to 10 bedrooms. Commercial and industrial properties have different requirements and calculations for septic tank sizing.
  6. What should I do if my calculated septic tank size is larger than the available space on my property? If the calculated septic tank size is larger than the available space on your property, you may need to consider alternative waste treatment solutions or consult with a professional to explore options that comply with local regulations.

Remember, this septic tank size calculator provides a general estimate based on standard guidelines. For more accurate calculations or specific requirements, it is always recommended to consult with a professional in the field or refer to local building codes and regulations.

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