Septic Tank Size Calculator
Calculate required septic tank size based on number of bedrooms and daily water usage.
Results
Visualization
How It Works
Septic tank sizing is primarily based on the number of bedrooms (which determines potential occupancy) plus daily water usage. Most codes require a minimum 1,000 gallon tank for 3 bedrooms.
The Formula
Base Size: 1-2 BR = 750 gal, 3 BR = 1000 gal, 4 BR = 1250 gal, +250 per additional BR. Add 25% for garbage disposal.
Variables
- BR — Number of bedrooms (determines code minimum)
- GPD — Gallons per day of sewage flow
Worked Example
A 3-bedroom home with 4 occupants using 60 gal/day: Code minimum = 1000 gal, flow-based = 4 x 60 x 1.5 = 360 gal. Use 1000 gallon tank.
Practical Tips
- Septic tanks should be pumped every 3-5 years
- Garbage disposals increase sludge significantly — consider not using one
- Larger tanks mean less frequent pumping
- Drain field sizing is separate and based on soil percolation tests