Reference
Septic tank size chart by bedrooms
The standard tank size for each bedroom count, with the design flow behind it. Use the calculator below to adjust for a garbage disposal or high-efficiency fixtures.
| Bedrooms | Design flow (GPD) | Recommended tank |
| 1 | 150 | 1,000 gal |
| 2 | 300 | 1,000 gal |
| 3 | 450 | 1,000 gal |
| 4 | 600 | 1,250 gal |
| 5 | 750 | 1,500 gal |
| 6 | 900 | 2,000 gal |
Design flow = bedrooms × 150 GPD; floored at the 1,000-gal code minimum, rounded to a standard size.
Check your exact size
Estimate only. Your local health authority sets the legal minimum — always confirm before buying or installing a tank.
The standard
How to read the chart
Every row uses the same public standard: 150 gallons of design flow per bedroom per day, held for a 48-hour retention, then floored at the local code minimum (usually 1,000 gallons) and rounded up to a standard manufactured tank size — 1,000, 1,250, 1,500, 2,000, or 2,500 gallons.
Because small homes fall below the code minimum on raw flow, 1, 2, and 3-bedroom homes commonly share the same 1,000-gallon tank. The size only steps up once design flow exceeds the floor, around 4 bedrooms. For the reasoning on a specific home, see what size septic tank do I need.
Frequently asked questions
What is the standard septic tank size by bedrooms?
1,000 gallons up to 3 bedrooms, 1,250 for 4, 1,500 for 5, and 2,000 for 6 bedrooms. These are common baselines; high-use homes may need more.
How is the chart calculated?
Each row is bedrooms × 150 gallons/day of design flow, held for a 48-hour retention, then floored at the 1,000-gallon code minimum and rounded up to the nearest standard tank size.
Does the chart change with a garbage disposal?
A disposal adds about 250 gallons of solids capacity, which can move you to the next standard size — most noticeably at 4+ bedrooms. Use the calculator to see your specific case.
Are these sizes the same in every state?
No. The chart uses widely-adopted baselines, but individual states and counties set their own minimums and may require larger tanks. Always confirm locally.