Septic Tank Size Calculator

Tank size, drain field area and pumping schedule for your home.

Project Details
Enter your measurements and requirements
Results
Calculated estimates for your project
Recommended tank1,000 gal
Code minimum by bedrooms1,000 gal
Daily design flow450 gal/day
1.5 x daily flow675 gal
Pump about every2.6 years
Drain field (trench bottom)750 sq ft
Trench length at 3 ft wide250 ft

Turn these numbers into a build plan.

  • 1,000 gal tank
  • 750 sq ft drain field
  • 2.6 years pump about every

How we got this: the larger of the code minimum for your bedrooms and 1.5 x the daily design flow (150 gal per bedroom per day, or 75 per person if that is more), plus 250 gal for a disposal, rounded up to a standard tank. Codes vary by state and county.

Pump about every 2.6 years

Your 1,000 gal tank with 4 people needs pumping about every 2.6 years. Get a reminder so it never backs up into the drain field.

The calendar file repeats on that interval in Apple, Google and Outlook calendars. In Blueprint the pump date becomes a recurring maintenance task, with the tank size and last pump date saved to your home.

Sump and footing drains should never go to the tank; size a pump for them with the sump pump calculator. Planning a water heater too? See the tankless water heater calculator.

Next you will need

Sump Pump Size Calculator

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Project plan · built from your numbers

Plan a 1,000 gallon septic system

Sizing notes for a 1,000 gallon tank serving 3 bedrooms, with the permit, soil test, installer quotes and a pumping schedule about every 2.6 years. A licensed designer and your health department decide the final system.

Materials
$1,750
Time
2 to 3 months, mostly waiting on the permit
Level
Intermediate
6 steps 4 tools 4 materials
  1. 1

    Call your health department

    Ask which code applies, the minimum tank for 3 bedrooms and whether a licensed designer is required. These numbers are a starting point: the county has the final say.

    • Local minimum tank size written down
    • Designer requirement confirmed
    • Permit fees noted
  2. 2

    Map the site

    Sketch the house, well, property lines, slopes and driveways, with distances. Keep vehicles and new construction off any area that could become the drain field.

    • Well and water lines marked
    • Setbacks measured
    • Field area protected from traffic
  3. 3

    Get the soil tested

    Book a soil or perc test. This estimate assumes about 750 sq ft of trench bottom, and the real result can move that a lot.

    • Test booked
    • Report saved
01 · Your numbers
Tank
1,000 gal
Drain field
750 sq ft
Pump about every
2.6 years
Owner costs
$1,750
02 · The plan

6 steps · 4 tools · 4 materials

3 more steps, the full tool list and a shopping list you can check off as you go.

03 · Finished

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3/5

Plan a 1,000 gallon septic system

Finished in 2 to 3 months, mostly waiting on the permit · $1,750 DIY

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Septic tank size by bedrooms

Most US codes require at least 1,000 gallons for up to 3 bedrooms, 1,250 for 4 and 1,500 for 5. A 4 bedroom home with 5 people uses a 1,250 gallon tank and needs it pumped about every 2.6 years.

Typical US minimums without a disposal, Ontario OBC working capacity, and drain field in loam
BedroomsDesign flowUS tankLitresOntario (OBC)Drain field, loam
1150 gal/day1,000 gal3,790 L3,600 L250 sq ft
2300 gal/day1,000 gal3,790 L3,600 L500 sq ft
3450 gal/day1,000 gal3,790 L3,600 L750 sq ft
4600 gal/day1,250 gal4,730 L4,000 L1,000 sq ft
5750 gal/day1,500 gal5,680 L5,000 L1,250 sq ft
6+900 gal/day1,750 gal6,620 L6,000 L1,500 sq ft

What size septic tank for a 3, 4 or 5 bedroom house?

3 bedrooms: 1,000 gallons. 4 bedrooms: 1,250 gallons (1,000 to 1,250 depending on the state). 5 bedrooms: 1,500 gallons. Add about 250 gallons for a garbage disposal or a large soaking tub, and size up if more than two people share each bedroom.

How the septic tank size is calculated

Tank = max(code minimum, 1.5 x daily design flow) + disposal allowance, rounded up to a standard size.

  1. Find the daily design flow. Most US codes use 150 gallons per bedroom per day; Ontario uses OBC Table 8.2.1.3.A (1,600 L a day for 3 bedrooms).
  2. Take the larger of the code minimum and the flow rule. US: at least 1,000 gal for up to 3 bedrooms, 1,250 for 4, 1,500 for 5, and 1.5 x daily flow. Ontario: 2 x daily flow and at least 3,600 L.
  3. Add for a disposal and round up. Add about 250 gal for a garbage disposal (some states require 50% more), then round up to the next standard tank size.

Worked example: a 4 bedroom home with 5 people. Design flow is 4 x 150 = 600 gal a day; 1.5 x 600 = 900 gal, which is under the 1,250 gal minimum for 4 bedrooms, so the tank is 1,250 gal (1,500 with a disposal). Codes vary: the EPA guidance, the IRC appendix your state adopted, and Ontario's OBC Part 8 all differ, so confirm with your county health department or a licensed designer.

Septic drain field size calculator

Drain field area = daily design flow / soil application rate. Divide by 3 for the length of 3 ft wide trenches.

SoilApplication rate
Sand or gravelly sand (perc 1 to 5 min/in)1.2 gal per sq ft per day
Sandy loam (6 to 15 min/in)0.8 gal per sq ft per day
Loam (16 to 30 min/in)0.6 gal per sq ft per day
Silt loam (31 to 45 min/in)0.45 gal per sq ft per day
Clay loam (46 to 60 min/in)0.3 gal per sq ft per day
Clay (over 60 min/in)0.2 gal per sq ft per day

Perc rates slower than about 120 minutes per inch, high groundwater or shallow bedrock need an engineered mound or drip system.

How often to pump a septic tank: chart

Years between pumpings, Penn State Extension. A garbage disposal shortens each interval by about a third.
Tank1 person234568
750 gal9.14.22.61.81.310.6
1,000 gal12.45.93.72.621.51
1,250 gal15.67.54.83.42.621.4
1,500 gal18.99.15.94.23.32.61.8
1,750 gal22.110.76.953.93.12.2
2,000 gal25.412.485.94.53.72.6
2,250 gal28.6149.16.75.24.23
2,500 gal31.915.610.27.55.94.83.5

Whatever the chart says, have the tank inspected at least every 3 years. Keep grease, wipes and harsh cleaners out of it, and route sump and gutter water away from the drain field (the basement waterproofing cheat sheet covers grading and drains).

Canada and Ontario septic tank sizes

The Ontario Building Code sizes a residential tank at 2 x the daily design flow with a 3,600 L minimum, so a 3 bedroom home needs 3,600 L and a 4 bedroom home 4,000 L. Other provinces use similar flow tables; pick Ontario and litres in the calculator.

More plumbing help

Start with the plumbing cheat sheet, check the garbage disposal installation guide before adding one on septic, and size pipes with the PEX sizing chart.

Septic tank size FAQ

What size septic tank do I need for a 4 bedroom house?

A 4 bedroom house needs at least a 1,250 gallon tank in most US states (4,730 L), and 1,500 gal with a garbage disposal. In Ontario it is 4,000 L.

What size septic tank for a 3 bedroom house?

1,000 gallons is the usual minimum for 1 to 3 bedrooms. With a disposal or more than 6 people, go to 1,250.

What size septic tank for a 5 bedroom house?

1,500 gallons in most US codes, plus about 250 for a disposal. Ontario's 2 x flow rule gives 5,000 L.

How big is my septic tank?

Check the permit or as-built drawing at your county health department first. Otherwise, measure the inside length, width and liquid depth when it is opened for pumping, and use the measure mode: cubic feet x 7.48 = gallons.

What is the septic tank capacity per person?

Plan on 75 to 100 gallons per person per day of wastewater. Codes size by bedrooms instead (150 gal per bedroom per day) because the number of people changes over a house's life.

What is the average septic tank size?

1,000 to 1,250 gallons for a typical 3 to 4 bedroom home in the US, and 3,600 to 4,500 L in Canada.

How often should a septic tank be pumped?

Every 3 to 5 years for a typical family, but it depends on tank size and people: a 1,000 gal tank with 4 people needs it about every 2.6 years. The chart below and the calculator give your interval.

How big should a drain field be?

Divide the daily design flow by the soil's application rate. A 3 bedroom home (450 gal a day) in loam at 0.6 gal per sq ft needs about 750 sq ft of trench bottom, 250 ft of 3 ft trench; in clay it is over 2,000 sq ft.

Does a garbage disposal need a bigger septic tank?

Yes. A disposal adds about 50% more solids, so add 250 gal (some states require 50% more capacity) and pump more often. See the garbage disposal installation cheat sheet before adding one to a septic home.

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