Septic information online is a mess. State health department PDFs are accurate but written for inspectors, contractor blogs are usually written to close a sale, and forum threads from 2009 still rank for questions homeowners ask in 2026. We built this site to be the reference we wished existed when we first started chasing down tank sizes, perc rates, and county setbacks ourselves.
What We Do
SepticCalculator.com is a free reference for anyone trying to size, plan, maintain, or evaluate a septic system. Everything on the site works without an account, an email signup, or a request for your phone number.
The calculators cover the four numbers that most people need to put on paper before they call a designer or installer. The tank sizing tool maps bedroom count and disposal use to minimum tank capacity. The drainfield calculator translates soil type and bedroom count into required absorption area. The cost estimator pulls together regional install ranges, soil-driven adders, and the cost of advanced treatment when a site needs it. The pump schedule tool gives you a realistic interval based on tank size and household size, since the old "every three years" rule of thumb misleads as often as it helps.
The state pages cover all 50 states. Each one summarizes the agency that issues permits, the minimum tank sizes set in code, the soil-based drainfield sizing rules, and the local quirks that catch people off guard: coastal setbacks in Florida, frost depth in Minnesota, mound system requirements in Wisconsin, and water-saving rules in California.
The guides are longer reads on the topics that come up over and over: how septic systems actually work, what maintenance schedule keeps a system out of trouble, how to read a soil test, what a healthy drainfield looks like, how to diagnose common failures, and what a fair price looks like for a new install or repair.
Why We Built This
Most homeowners only think about septic when something goes wrong, when a real estate transaction forces an inspection, or when they are pricing a new build on a lot without sewer access. At that point they have a week or two to make decisions that will outlast the roof on their house, and the available reading is scattered, dated, or quietly trying to sell them something.
State and county codes are the source of truth, but they are not pleasant reading. A typical state OWTS rule runs sixty to two hundred pages, references a half dozen other code sections, and assumes the reader already knows what a SAR loading rate or a pressure dosing manifold is. Reading them cold is a poor use of a Saturday afternoon.
Contractor sites usually do a better job of plain language but vary wildly in quality, and many are tuned to drive a quote request rather than answer the question. Forums and Reddit threads can be excellent or wildly wrong, and you have no easy way to tell which is which.
We wanted one place where the rules, the math, and the explanations live side by side. The state pages and the calculators pull from the same data set, so if your state requires 1,500 gallons for a four-bedroom home, you see that number in the state guide, in the calculator output, and in the underlying source notes. No surprises, no contradictions.
How Our Calculators Work
The state code data comes from each state's department of health, environmental quality agency, or equivalent. We track the published minimum tank capacities, drainfield sizing tables, soil classification rules, setback distances, and any state-level requirements for advanced treatment. When a state delegates most of its rule-making to counties, we note that and show the most common county-level standards rather than pretending a single number applies statewide.
Soil absorption rates come from the loading rate tables that appear in nearly every state OWTS code, originally based on the EPA Onsite Wastewater Treatment Systems Manual and decades of field data from university extension programs. Those rates translate inches-per-minute percolation into square feet of drainfield per bedroom. The numbers are conservative on purpose, since drainfields fail when they are undersized and rarely when they are oversized.
Tank sizing uses bedroom count as the demand proxy, because peak daily flow correlates more reliably with bedrooms than with current occupancy. A two-person household in a four-bedroom home still needs a four-bedroom tank, since the next owner may have four kids.
Cost ranges come from a combination of state extension publications, public bid data, and contractor pricing surveys. Costs vary enormously by region, soil, and access, so the calculators give you a range with the drivers explained, not a single false-precision number.
These calculators are estimators. They are accurate enough to budget a project, sanity-check a quote, or compare two lots before you buy. They are not stamped designs, and they cannot replace a perc test or a licensed designer's site visit.
Who This Is For
We had four readers in mind while building this.
Homeowners planning a new build on land without sewer service, who need to figure out whether the lot will perc, what kind of system it will support, and roughly what the bill will be. The state page plus the four calculators usually answers most of the early questions before a single contractor visit.
Current owners trying to keep an existing system healthy, who want to know how often to pump, what to put down the drain (and what to keep out), and how to spot trouble before the lawn turns into a swamp.
Real estate buyers and sellers evaluating a property where septic is part of the deal. The state page tells you what code looked like when the system was likely permitted, the calculators tell you what would be required if the system had to be replaced today, and the troubleshooting guide helps you read a septic inspection report.
Contractors, inspectors, and code officials who want a fast cross-reference to another state's minimums without digging through that state's full rule set. Our state pages will not replace your local code, but they make it easy to answer a quick question from a client who is moving across the country.
What We're Not
We are not licensed engineers, soil scientists, or installers, and the site is not a substitute for any of them. A real percolation test, performed on your specific lot by a qualified professional, will tell you things our soil-type dropdown cannot.
Local rules can be (and often are) stricter than state minimums. County health departments routinely add setback requirements, mandate alternative systems in sensitive watersheds, or require specific tank materials. Always confirm with the agency that issues permits in your county before you commit to a design.
Permits, stamped designs, and final installation belong with licensed professionals. The calculators help you arrive at the conversation prepared, not skip the conversation.
We run advertising on the site, and the ads are how we keep everything else free. We are not a contractor referral network, we do not take fees from installers for ranking, and nothing on the site is a paid placement. If a page reads like a sales pitch for a particular product or company, it is not from us.
Get in Touch
If you spot an error in a state page, a calculator output that looks off for your area, or a topic the guides should cover, write to us at [email protected]. The contact page on the site has the same address and a short form. We read every message, and corrections from working contractors and county staff are especially welcome.