Septic Tank Size Calculator
By SepticReference Editorial TeamReviewed: Sources checked: 4 min read
Quick answer
Most homes with up to 3 bedrooms need a 1,000-gallon septic tank. Four bedrooms usually need 1,000–1,500 gallons, depending on the state. Your state code sets the legal minimum by bedrooms. A larger household or a garbage disposal can justify going one or two sizes bigger so the tank lasts 3+ years between pumpings.
Recommended tank size
1,250 gal
- Typical state minimum
- 1,000 gal
- Sized for your household
- 1,250 gal
Example 1,250-gallon tanks (outside dimensions, L × W × H)
- 9′8″ × 4′7″ × 5′10″ — polyethylene, Norwesco Legacy 1250
- 13′1″ × 5′0″ × 4′3″ — polyethylene, Norwesco Low Profile 1250
- 10′5″ × 5′1″ × 6′0″ — concrete, Jensen Precast PJS 1250
Your permit sets the legal size. Use this to check a quote or plan a budget.
How we calculated this
- Typical state minimum for 3 bedrooms: 1,000 gal (median of 8 state codes we verified; range 900–1,500 gal).
- Smallest standard tank that gives 4 people at least 3 years between pumpings: 1,250 gal.
Sources used
- Minn. R. 7080.1930 Septic Tank Capacity — Minnesota Office of the Revisor of Statutes (MPCA rule)
- Ohio Adm. Code 3701-29-12 (copy at Cornell LII) — Cornell Law School LII
- 25 Pa. Code § 73.31 Estimating sewage flows — Pennsylvania Code & Bulletin
- S.C. Code Regs. R. 61-56.201 (copy at Cornell LII) — Cornell Law School LII
- Tenn. Comp. R. & Regs. 0400-48-01-.08 (copy at Cornell LII) — Cornell Law School LII
- 12VAC5-610-815 Septic tank capacity (Sewage Handling and Disposal Regulations) — Virginia Legislative Information System
- WAC 246-272A-0232 Design requirements — Septic tanks — Washington State Legislature
- Wyo. Code R. 020.0011.25 Small wastewater systems, septic tanks (copy at Cornell LII) — Cornell Law School LII
- Septic Tank Maintenance (EC 1343) — Oregon State University Extension Service
- Septic Tank/Soil Absorption Field (L-5227) — Texas A&M AgriLife Extension
- Septic System Maintenance (AEX-740) — Ohio State University Extension (Ohioline)
- Septic Tank Maintenance: A Key to Longer Septic System Life (MF-947) — Kansas State University Research and Extension
- Septic Tank Pumping — Penn State Extension
- How to Care for Your Septic System — US EPA
- Norwesco Water & Waste Management Catalog (2020) — Norwesco, Inc.
- Pedestrian Rated Septic Tank - 1250 gal - Baffle Access - AZ Market — Jensen Precast (Jensen Infrastructure)
On this page
How to use this calculator
- Pick your state. States marked ✓ have a tank-size table we verified in the state code. For other states the calculator shows the typical minimum across the codes we verified.
- Enter bedrooms. This is what the permit is based on. Count every room that could be used as a bedroom, as your county will.
- Enter the number of people if more people live there than bedrooms + 1. This doesn’t change the legal minimum, but it can change the size we recommend.
- Tick garbage disposal or large tub if they apply.
The result shows three numbers:
- Code minimum: what the bedroom table requires.
- Sized for your household: the smallest tank that gets your household to at least 3 years between pumpings.
- Recommended size: the larger of the two, adjusted for a disposal and rounded up to a standard tank size.
How we calculate the size (methodology)
Most calculators online take bedrooms and give you a single number with no explanation. Ours uses three published rules, and every result has a “How we calculated this” panel listing the exact sources.
1. The code minimum by bedrooms
State rules set the smallest tank allowed for each bedroom count. These are the tables we have verified so far:
| State | 2 BR | 3 BR | 4 BR | 5 BR | Each extra BR |
|---|---|---|---|---|---|
| Minnesota | 1,000 | 1,000 | 1,500 | 1,500 | Table to 9 BR, then +250 |
| Ohio | 1,000 | 1,500 | 2,000 | 2,000 | — |
| Pennsylvania | 900 | 900 | 1,250 | 1,400 | — |
| South Carolina | 1,000 | 1,000 | 1,000 | 1,250 | +250 |
| Tennessee | 750 | 900 | 1,000 | 1,250 | +250 |
| Virginia | 750 | 900 | 1,200 | 1,500 | — |
| Washington | 1,000 | 1,000 | 1,000 | 1,250 | +250 |
| Wyoming | 1,000 | 1,000 | 1,000 | 1,150 | +150 |
If your state isn’t verified yet, we show the median of these tables for your bedroom count and label it as such. Your county health department sets the real legal minimum. We are adding states as we verify them against the regulator’s own code.
2. A household check: at least 3 years between pumpings
EPA recommends having a household septic system inspected at least every three years and notes that tanks are typically pumped every three to five years. We use the standard extension pumping table (Mancl, published by Oregon State, Texas A&M and Ohio State) to find the smallest standard tank that gives your actual household at least 3 years between pumpings. This is why a family of six in a 2-bedroom house gets a bigger recommendation than the 2-bedroom code minimum.
3. Garbage disposal: +50%
Minnesota’s rule requires a tank at least 50% larger when a garbage disposal is installed or planned. Clemson Extension notes that disposals can add up to 50% more solids. In Minnesota we apply this to the legal minimum. In other states we apply it to the recommendation only, and say so.
4. Round up to a standard size
Tanks are sold in standard sizes: 750, 1,000, 1,250, 1,500, 1,750, 2,000 and 2,500 gallons are common. We round up, never down. Example dimensions come from manufacturer spec sheets (Norwesco plastic tanks; Jensen Precast concrete tanks).
Worked examples
3 bedrooms, 4 people, Virginia, no disposal. Virginia’s minimum for 3 bedrooms is 900 gallons. For 4 people, the pumping table gives about 2.3 years for 900 gallons and 2.6 years for 1,000 gallons. A 1,250-gallon tank gives 3.4 years, so the calculator recommends 1,250 gallons. The legal minimum is still 900. The extra capacity buys you longer gaps between pumpings.
4 bedrooms, 5 people, Washington, garbage disposal. Washington’s minimum is 1,000 gallons for up to 4 bedrooms, and 1,500 with a 50% disposal allowance. For 5 people with a disposal, a 1,750-gallon tank reaches only about 2.6 years between pumpings, while 2,000 gallons reaches 3 years. Recommendation: 2,000 gallons.
3 bedrooms, 3 people, state not verified yet. The typical minimum across verified states is 1,000 gallons. A 1,000-gallon tank gives 3 people about 3.7 years between pumpings. Recommendation: 1,000 gallons.
What this calculator does not decide
- The drain field. Tank size and drain-field size are separate. The drain field depends on soil percolation and design flow, and is set by a soil evaluation and your permit.
- Alternative systems. Aerobic units, mound systems and pump tanks often have their own sizing rules and manufacturer requirements.
- Your permit. The permit issued by your state or county is the only legal size. Use this calculator to check a design or a quote, not to replace either.
Septic tank sizes and dimensions
Real tanks of the same capacity differ in shape. Low-profile tanks are longer and shallower for sites with a high water table or shallow bedrock.
| Capacity | Material / model | Length | Width | Height |
|---|---|---|---|---|
| 750 gal | Plastic, Norwesco Legacy | 96 in | 52 in | 62 in |
| 1,000 gal | Plastic, Norwesco Legacy | 102 in | 60 in | 63 in |
| 1,000 gal | Plastic, Norwesco Low Profile | 127 in | 60 in | 51 in |
| 1,000 gal | Concrete, Jensen JS 1000 | 98 in | 64 in | 69 in |
| 1,250 gal | Plastic, Norwesco Legacy | 116 in | 55 in | 70 in |
| 1,500 gal | Plastic, Norwesco Legacy | 135 in | 55 in | 70 in |
| 1,500 gal | Concrete, Jensen JS 1500 | 128 in | 70 in | 69 in |
Already have a tank? Use the pumping frequency calculator to see how often it needs pumping, or read how often to pump a septic tank. Planning a new system? The septic system cost calculator estimates the whole project. Replacing an old tank? See septic tank replacement cost, and check the soil first with a perc test.
Frequently asked questions
What size septic tank do I need for a 3-bedroom house?
In most states the minimum is 900 to 1,000 gallons for 3 bedrooms. Virginia, Pennsylvania and Tennessee list 900 gallons. Minnesota, Washington, South Carolina and Wyoming require 1,000 gallons, and Ohio lists 1,500 gallons. For a family of four, a 1,250-gallon tank gives about 3.4 years between pumpings, versus about 2.6 years for 1,000 gallons.
What size septic tank do I need for a 4-bedroom house?
State minimums for 4 bedrooms range from 1,000 gallons (Washington, Tennessee, South Carolina, Wyoming) to 1,200 (Virginia), 1,250 (Pennsylvania), 1,500 (Minnesota) and 2,000 (Ohio). Your county health department applies your state’s table when it issues the permit.
How big is a 1,000-gallon septic tank?
It depends on the maker and material. A Norwesco Legacy 1,000-gallon plastic tank is about 102 × 60 × 63 inches (8.5 × 5 × 5.25 ft). A Jensen Precast 1,000-gallon concrete tank is about 98 × 64 × 69 inches. Low-profile tanks are longer and shorter.
Do I need a bigger septic tank if I have a garbage disposal?
Often, yes. Minnesota’s rule requires a tank at least 50% larger when a garbage disposal is installed or planned. Clemson Extension notes disposals can add up to 50% more solids. Even where it isn’t required, plan on pumping more often or choosing a larger tank.
Is a bigger septic tank better?
A larger tank holds more sludge, so it goes longer between pumpings. In the extension pumping table, 4 people get about 2.6 years from 1,000 gallons and 4.2 years from 1,500 gallons. It does not make a failing drain field work, and the drain field is sized separately.
Why do codes size septic tanks by bedrooms instead of people?
The number of people in a house changes over time, but bedrooms don’t. Codes assume a fixed flow per bedroom (Minnesota uses 150 gallons per bedroom per day), so the system still works for the next owner.
Related pages
Sources
Checked November 4, 2026. We cite primary sources only — see our editorial policy.
- Minn. R. 7080.1930 Septic Tank Capacity — Minnesota Office of the Revisor of Statutes (MPCA rule)
- 12VAC5-610-815 Septic tank capacity (Sewage Handling and Disposal Regulations) — Virginia Legislative Information System
- WAC 246-272A-0232 Design requirements — Septic tanks — Washington State Legislature
- Septic Tank Maintenance (EC 1343) — Oregon State University Extension Service
- How to Care for Your Septic System — US EPA
- Be Septic Safe — Clemson University Cooperative Extension (Water Resources)
- Norwesco Water & Waste Management Catalog (2020) — Norwesco, Inc.
- Pedestrian Rated Septic Tank - 1000 gal - End Access - Tuf-Tite Lid — Jensen Precast (Jensen Infrastructure)