Septic Tank Size Calculator
Find the septic tank capacity your home needs by bedroom count.
What you'll need to order
- septic tank
- distribution box
- perforated leach pipe
- drain rock
- filter fabric
Prices vary by region and haul distance. Get quotes from at least two local suppliers.
How this calculator works
tank gallons = 750 + (bedrooms − 2) × 250
Local health codes vary considerably and always override this figure. The drain field calculation depends entirely on a percolation test — soil type changes the required area by a factor of four.
Worked example
With number of bedrooms 3 , daily flow per bedroom 150 , soil loading rate 0.5 , this calculator returns 1000 gal.
Frequently asked questions
What size septic tank do I need for a 3 bedroom house?
One thousand gallons is the common code minimum. Four bedrooms takes 1,250 and five takes 1,500. Your local health department sets the binding figure.
Why are septic systems sized by bedrooms?
Bedrooms indicate potential occupancy rather than current occupancy. A system sized for two people in a four bedroom house would fail the moment the property changed hands.
How big does the drain field need to be?
It depends entirely on soil percolation. The same 450 gallon daily flow needs 560 sq ft in sand but 2,250 sq ft in clay. Only a percolation test can determine it.
How often does a septic tank need pumping?
Every three to five years for a typical household. Longer intervals let solids carry over into the drain field, and a failed field costs many times what a lifetime of pumping does.