A septic tank size chart is two tables, not one. The first is the bedroom minimum most US codes start from. The second is the list of tanks precast plants actually pour. The calculator on the homepage runs both, plus a 48-hour retention floor, and tells you which rule won. This page is those tables in one place, so you can read the row before you set the sliders.
Minimum tank size by bedrooms
This is the common US baseline, the one the EPA onsite manual and most state codes start from. One to three bedrooms share a 1,000 gallon floor. Each bedroom after that adds 250 gallons. A verified state uses its own table: Florida, North Carolina, Georgia, California, Pennsylvania and Texas are on file. Everywhere else the table below is the starting point, not the permit.
| Bedrooms | Minimum tank | Design flow | Two-day retention |
|---|---|---|---|
| 1 to 3 | 1,000 gal | 240 to 360 gpd | 480 to 720 gal |
| 4 | 1,250 gal | 480 gpd | 960 gal |
| 5 | 1,500 gal | 600 gpd | 1,200 gal |
| 6 | 1,750 gal | 720 gpd | 1,440 gal |
| Each extra | +250 gal | +120 gpd | +240 gal |
Design flow is 120 gallons per bedroom per day on the EPA midpoint. Two days of that flow is the retention number. Look at the 3 bedroom row: retention is 720 gallons, the bedroom table is already 1,000, so the bedroom table wins. Look at the 5 bedroom row: retention is 1,200, the bedroom table is 1,500, so the bedroom table still wins. Retention beats the table only when occupants, not bedrooms, drive the flow.
Stock sizes plants actually pour
A computed 1,100 gallons does not exist as a product. The calculators on this site snap up to the next size on this list: 500, 750, 1,000, 1,250, 1,500, 1,750, 2,000, 2,500 and 3,000 gallons. 500 is a pump chamber or an inherited problem. 750 is the same in most states. California's Tier 1 table does use 750 gallons for a one or two bedroom house.
| Size | Typical L x W x H | Typical weight | Usual house |
|---|---|---|---|
| 500 gal | 5 to 8 ft x 4 to 5.5 ft x 4 to 5 ft | 4,400 to 6,000 lb | Pump chamber only |
| 1,000 gal | 8 to 8.5 ft x 5 to 5.7 ft x 5 to 5.3 ft | 8,000 to 8,600 lb | 1 to 3 bedrooms |
| 1,250 gal | 9 to 10.5 ft x 5.5 to 6 ft x 5 to 5.5 ft | 9,000 to 11,000 lb | 4 bedrooms |
| 1,500 gal | 10 to 12 ft x 5.5 to 6 ft x 5 to 5.7 ft | 10,750 to 12,500 lb | 5 bedrooms |
| 2,000 gal | 11.5 to 13 ft x 6 to 6.5 ft x 5.5 to 6 ft | 14,000 to 16,000 lb | Large house or long interval |
Two plants twenty miles apart will not share a hole. Use this chart to see whether a truck can reach the yard, not to stake the excavation. The 1,000 gallon page is the product page for the default residential tank. The 1,500 gallon page is the next size people actually mean.
How to read a row for your house
- Start with bedrooms, not today's occupants. Codes size on the house, because the next family may be larger.
- Fill occupants only when the house is more crowded than the bedroom count implies. Flow then uses 60 gallons per person per day if that number is larger.
- Take the larger of the bedroom table and two days of flow. Then snap up to a stock size.
- Check the state picker. A verified state can raise the floor. An unverified state still shows this chart and says so.
The county sizes against its own table, its own setbacks and a soil evaluation of the actual yard. A garbage disposal, a high-occupancy house or a stricter state can move you up a row. Run the septic tank size calculator with your bedrooms and occupants, then ask the bidder where their table differs.
2, 3 and 4 bedroom houses on this chart
A two bedroom and a three bedroom house land on the same 1,000 gallon tank. That is the code floor, not a rounding error. A four bedroom house steps to 1,250. Slow soil does not change the tank row. It changes the drainfield. If the field is the question, the drain field size calculator is the other half of this chart.