Last updated: May 3, 2026
Septic tank size calculator
Tell us your bedroom count, occupancy profile, and tank type. Get a recommended tank size, expected pump interval, and 2026 SD County install price band — calibrated to county DEH sizing rules.
Want a real site evaluation and DEH-approved design? We handle the perc test, the permit, and the install end-to-end.
Call (858) 808-6055How this works. Tank-size recommendations follow SD County DEH minimums per bedroom, with an upward adjustment for higher-load households. Pump intervals are calibrated from average residential solids production data. The price band reflects 2026 SD County install pricing for like-for-like tank replacement, fully permitted. New full-system installs (tank + drain field) run higher.
FAQ
How does this calculator work?
It uses SD County DEH minimum tank-size rules (driven by bedroom count) plus a load adjustment for occupancy and disposal use to give you a recommended capacity, an expected pump interval, and a cost band for new installations. The pump interval estimate is based on average household solids production calibrated to SD County data.
Is this a substitute for a real DEH design?
No. New installs require a county-approved design that factors in soil class, slope, setbacks, and site constraints. Replacements often follow the same sizing as the existing tank unless you are adding bedrooms. This calculator is a sanity-check estimate, not an installation drawing.
Why does adding a garbage disposal change the answer so much?
A garbage disposal roughly doubles the solid waste reaching the tank. SD County DEH actually requires a 50% larger tank for homes with disposals on new installs — and pump intervals shrink correspondingly. If you have a disposal and a small tank, you should probably pump more often than the calendar suggests.
Why is my actual tank smaller than the recommendation?
Older homes were sized to the standards in effect at the time, which were less strict than today. A 1,000-gallon tank serving a 4-bedroom home is undersized by current code but not illegal — until you replace the tank. At replacement time, you must size to current code.
How do I know when to replace versus repair my existing tank?
Tanks under 25 years old with localized damage almost always favor repair. Tanks 30+ years old with multiple failures, structural cracks at the seam, or steel tanks with rust-through favor replacement. We give you both numbers when we quote.
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