Septic Tank Size Calculator

Under NYS75-A Table 3, a 4-bedroom house needs a minimum 1,250-gallon tank, which is about 4,732 litres. In the UK, the same house (6-person equivalent) needs 150 x 6 + 2,000 = 2,900 litres, about 766 gallons, per British Water Flows and Loads. Always round up to the next manufactured size and confirm with your local health department.

The conservative code value used in California, Missouri, Arizona, and Kansas is 150 gallons per day per bedroom. New York refines this by fixture vintage in Table 1: 90 gpd per bedroom for modern water-saving fixtures, 110 for post-1994, 130 for pre-1994, and 150 for pre-1980 fixtures.

Use tank volume = max(1,000 gallons, 1.5 x daily flow in gpd), then round up to the next standard size (New York intermediate-systems rule). Example: 3 bedrooms x 150 gpd = 450 gpd, so 1.5 x 450 = 675 gallons, which rounds up to the 1,000-gallon minimum. For 4 bedrooms: 600 gpd gives 900 gallons, also rounded up to 1,000 gallons - though the bedroom method requires 1,250 gallons for 4 bedrooms, so the larger value governs.

Yes, in New York it does. NYS75-A counts a garbage grinder as equivalent to one additional bedroom, so a 3-bedroom house with a disposal is sized as a 4-bedroom house: 1,250 gallons instead of 1,000. It also adds solids, so pump-outs come sooner.

TCEQ Table III rates a 4-bedroom house at 300 gpd with water-saving fixtures. Table II then assigns 251-350 gpd to a 1,000-gallon tank, so the code minimum for 4 bedrooms in Texas is 1,000 gallons. Larger flows step up: 351-500 gpd needs 1,250 gallons, and above 500 gpd the tank is 2.5 x daily flow.

British Water Flows and Loads sizes by population: minimum tank = 150 litres x people + 2,000 litres. A 1-3 bedroom house counts as 5 people, so 150 x 5 + 2,000 = 2,750 litres; a 4-bedroom house counts as 6 people, giving 2,900 litres; a 5-bedroom house gives 3,050 litres (about 806 gallons). Round up to the next manufactured tank.

Divide daily flow by the soil long-term application rate. Texas rates: gravel/coarse sand 0.50, coarse sand 0.38, sandy loam 0.25, clay loam 0.20, clay 0.10 gpd per sq ft. Example: 600 gpd on sandy loam needs 600 / 0.25 = 2,400 sq ft (about 223 m2), which is 1,200 linear feet of 2-ft-wide trench. Most codes also require a 100% reserve area.

Use the Mancl pumping-frequency table (Ohio State Extension): a 1,000-gallon tank serving 4 people needs pumping about every 2.6 years; a 1,500-gallon tank with 4 people about every 4.2 years; a 1,250-gallon tank with 4 people about every 3.4 years. Garbage disposals and heavy use shorten the interval; inspect sludge depth yearly.

A typical precast-concrete 1,000-gallon tank is about 8 ft x 5 ft 8 in x 5 ft 2 in (outside). A 1,500-gallon tank is about 10 ft x 6 ft 4 in x 6 ft, and a 2,000-gallon tank about 12 ft 4 in x 6 ft 6 in x 6 ft 4 in. Dimensions vary by manufacturer and material, so confirm with your supplier before excavating.

No. This tool gives planning estimates from published code tables (NYS75-A, TCEQ, British Water, and others) for the US and UK. Real systems need a site evaluation, percolation test, and a permit from your local health department, which may be stricter than these tables. Never install or buy a system on this estimate alone.