Septic Tank Size Calculator
Estimate the required septic tank capacity based on number of bedrooms, occupants, and daily water usage.
Published by:
isCalculator Editorial Team
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How to use this tool?
How to Use the Septic Tank Size Calculator
- Enter the number of bedrooms in the first field. This helps estimate household size.
- Enter the number of occupants (people living in the home).
- Enter daily water usage per person in gallons (default is 70 gallons).
- Click the "Calculate" button.
What the result means:
- The calculator multiplies occupants × daily usage per person, then applies a 1.5 safety factor.
- The result is the recommended septic tank size in gallons (imperial units).
- A minimum of 1,000 gallons is enforced.
Note: All inputs must be whole numbers of 1 or more. Invalid entries will show an error.
Previous Results
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Frequently Asked Questions
The calculator uses the formula: (Number of Occupants × Daily Water Usage per Person) × 1.5 safety factor, with a minimum of 1000 gallons.
Key factors include the number of bedrooms, actual occupants, and daily water usage per person. Local regulations may also require specific minimums.
While a larger tank provides more capacity and longer intervals between pumping, it's important to size it appropriately to avoid excessive cost and inefficient operation.