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Septic answers that cite the actual rule
Most septic calculators give you a national average and a lead form. This one applies your own state's code — design flow, tank table, detention rule, setbacks — and shows you the citation, so you can check it.
50 state codes · 99 primary sources · no contractor referral fees
7 calculators, all instant
Every one updates as you type. None of them ask for your email.
Septic Tank Size Calculator
Find the minimum tank capacity your state code requires, plus the size a designer would actually specify for your household.
Open →Drainfield Size Calculator
Calculate absorption area from your soil’s percolation rate or texture class, with trench length and mound alternatives.
Open →Septic System Cost Calculator
Build a line-item install estimate — tank, drainfield, excavation, permits, and design — adjusted for your state.
Open →Pumping Schedule Calculator
Work out how many years you have before sludge reaches the outlet baffle, using the EPA solids-accumulation model.
Open →Household Water Use Estimator
Estimate the daily flow your system has to treat — the number every other septic calculation depends on.
Open →Septic vs Sewer Comparison
Compare thirty years of owning a septic system against connecting to a public sewer, with every assumption editable.
Open →Percolation Test Calculator
Convert raw perc-test drop readings into a minutes-per-inch rate and the loading rate it implies.
Open →Why the state matters more than you think
The same three-bedroom house, priced the same way, in three states:
| State | Design flow | Tank required | Typical install |
|---|---|---|---|
| Tennessee | 450 gpd | 1,000 gal | $6,000 – $17,000 |
| Georgia | 450 gpd | 1,000 gal | $6,000 – $16,000 |
| Ohio | 360 gpd | 1,500 gal | $9,000 – $26,000 |
| Massachusetts | 330 gpd | 1,500 gal | $18,000 – $45,000 |
Same house. Twice the tank and three times the cost, purely because of where it sits.Compare all 50 states →
13 guides
Written for the homeowner who has just been told they need a new system and has no idea what any of it means.
How a septic system actually works
Tank, field, and soil — what each part does, how they fail, and why the soil is doing most of the work.
What a septic system really costs
Full breakdowns for install, repair, and 30-year ownership — plus how to read a suspiciously cheap quote.
Septic or sewer: the whole arithmetic
Both industries quote the half of this comparison that suits them. Here is all of it.
Drainfields: the expensive half
The part that costs the most and fails first. How it works, how it dies, and how to delay that.
Maintenance and pumping
What to do, when, what it costs — and which products are a waste of money.
Soil evaluation and perc testing
The test that decides whether your project costs $9,000 or $35,000.
Repair it or replace it?
The question every failing system eventually asks. Here is how to answer it without guessing.
Buying a house with a septic system
The due diligence list, the questions that actually matter, and the findings worth walking away from.
When something goes wrong
Read the symptoms, find the cause, know what it will cost before you call.
Selling a house with a septic system
What to fix before listing, what to disclose, and why a known defect costs more in negotiation than in repair.
Permits, inspections, and paperwork
Who approves what, how long it takes, and the inspection rules that catch sellers out.
Help paying for a septic system
Most people never ask. Failure repairs are exactly what these programmes exist to fund.
Which septic system will you need?
Seven system types, what each costs, and the soil conditions that decide for you.
Something is wrong right now
Start with what you can see. Every symptom page ranks the causes by how often each one actually turns out to be the answer, and prices all of them — because the useful information is nearly always that this is probably the $300 thing, not the $30,000 thing.
Priced job by job
What each individual piece of work costs, what the quote does and does not include, what moves the number, and whether you actually need it.
- Drainfield replacement $10,000–$40,000
- Tank replacement $3,000–$8,000
- Mound system $18,000–$45,000
- Aerobic unit (ATU) $12,000–$30,000
- Pumping $300–$700
- Inspection $250–$900
- Perc test $350–$1,800
- Sewer connection $3,000–$25,000
How this site is different
Septic content online is mostly written to capture a lead. The pattern is familiar: a national average, a vague range, and a form between you and the answer.
We took a different approach. Every sizing figure comes from the state rule it belongs to, and every state page lists the documents it was read from with the date it was checked. Where a state publishes its table only as a scanned image we could not read, we say so on the page rather than substituting a plausible number.
The calculators show their working — which rule governs, what the design flow is, what the loading rate assumption was — because a number you cannot check is a number you cannot use in a conversation with a contractor.