1,500-gallon septic tank dimensions

By Panyala · Last updated October 27, 2026 · How we write and review guides

A rectangular precast concrete 1,500-gallon septic tank is typically about 10.5 to 12.5 feet long, 5.5 to 6.5 feet wide, and 5 to 6 feet tall on the outside. Low-profile versions are longer and shorter. Exact sizes vary by manufacturer, so always plan from the spec sheet of the tank you're buying.

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Typical outside dimensions

The table below shows published dimensions for a few real 1,500-gallon concrete tanks. We picked them because the makers post full spec sheets. They show how much the shape can vary for the same capacity. This isn't a product recommendation.

So for planning, a 1,500-gallon concrete tank takes up a footprint of roughly 60 to 80 square feet and stands 5 to 6 feet tall. Your installer will dig the hole larger than the tank to leave room for bedding, backfill, and safe working space.

Why the outlet is lower than the inlet

Notice that in every example the outlet sits about 3 inches lower than the inlet. That drop keeps wastewater flowing from the house through the tank and out to the drain field by gravity. Inlet height also tells you how deep the tank has to be set for your house's sewer line to reach it with proper slope.

The volume math

One cubic foot holds about 7.48 gallons, so 1,500 gallons is about 200 cubic feet of liquid. A tank's outside dimensions are bigger than that because of:

• Wall, floor, and lid thickness, often around 3 to 6 inches of concrete
• Airspace above the liquid level, below the lid, where scum floats and gases collect
• The compartment wall, if the tank has two compartments

The rated capacity usually refers to the liquid volume below the outlet. If you're comparing tanks, compare the rated capacity on the spec sheet, not a number you work out from the outside dimensions.

Standard vs low-profile tanks

For the same capacity, a tank can be taller and shorter, or longer and lower. Low-profile tanks help where bedrock, a high water table, or a shallow sewer line makes it hard to dig deep. The trade-off is a larger footprint and, often, a higher price. If your site has shallow soil, ask the designer whether a low-profile tank or a different system design is needed.

Compartments and configurations

• Single compartment: one open chamber, now less common for new homes.
• Two compartments: a wall with an opening divides the tank, often with the first chamber larger. Some makers sell a 1,500-gallon tank split into 1,000 and 500 gallons.
• Two tanks in series: some systems use two smaller tanks instead of one large one, which can ease delivery on tight sites.
• Traffic-rated (H-20) versions: heavier tanks with thicker walls for driveways or parking areas.

Who needs a 1,500-gallon tank?

Codes usually size septic tanks by the number of bedrooms, because bedrooms predict how many people may live there. A common pattern, used by many state and county codes, is about 1,000 gallons for three bedrooms, 1,250 for four, and 1,500 for five. Some codes and cost guides are more generous and pair 1,500 gallons with six or seven bedrooms. Some codes also call for a bigger tank if you have a garbage disposal. The rules differ by state and county, so the local health department or your septic designer has the final word.

For a quick estimate for your home, try our septic tank size calculator.

Concrete vs plastic and fiberglass 1,500-gallon tanks

Plastic (polyethylene) and fiberglass tanks also come in 1,500 gallons. They're much lighter, so they can be delivered to sites a heavy boom truck can't reach. They're often a different shape, such as a longer, rounded tank, so check their dimensions separately. Light tanks need anchoring where groundwater is high, because an empty tank can float. See fiberglass septic tanks for the trade-offs and concrete septic tanks for other sizes.

What a 1,500-gallon concrete tank costs

• Tank only: Angi lists about $1,600 to $2,500 for a 1,500-gallon concrete tank (October 2026). The manufacturer price lists above show roughly $1,600 to $2,450 before delivery, setting, and tax, depending on the model.
• Replacing a tank, installed: our septic cost estimator shows about $3,000 to $9,500 for septic tank replacement, based on Angi and HomeGuide data. That doesn't include a new drain field.
• Pumping a 1,500-gallon tank: about $450 to $1,100, from the same sources, since many companies price by the gallon.

Delivery distance, excavation, rock, permits, soil tests, and risers can add a lot, so ask every installer for an itemized quote.

Site planning checklist

• Get the spec sheet: dimensions, weight, inlet and outlet heights, and number of compartments.
• Confirm setbacks from the house, well, property lines, and water, which come from local code.
• Check that the delivery truck has a clear, firm path, and look for overhead power lines.
• Plan risers so the tank can be pumped without digging. See septic tank risers and lids.
• Keep vehicles off the tank unless it's traffic-rated.

Sources: Shea Concrete septic tank price list (March 2026) and Juniata Concrete contractor price list (January 2026) for example dimensions and prices; Angi: concrete septic tank price; Angi and HomeGuide septic cost guides for replacement and pumping ranges, checked October 2026.