Offline
No internet, no account required.
IPC App.E
Validated against the standard.
PDF export
Pro-only. Generate professional reports.
$2.99 Pro
Lifetime unlock. No subscriptions.
How it works
Enter your values
Type in your inputs — the app fills code tables and constants for you, so there's nothing to look up.
Get a code-checked result
Instant answer with a clear PASS / FAIL and the exact IPC App.E reference behind every number.
Save & export
Keep a history of calculations and export a clean PDF report to share or attach to a permit (Pro).
What this calculator does
A septic system has two parts to size: the tank and the drainfield. This app sizes both — the tank from the number of bedrooms and the drainfield from the soil's percolation rate — following the conventions used by most health departments and the IPC appendix.
How it works
- Tank — sized by bedroom count, which stands in for daily flow (more bedrooms = larger minimum tank).
- Drainfield — sized from the percolation rate (minutes per inch) and the design flow; slower soils need more absorption area.
Worked example
A 3-bedroom home commonly requires a minimum 1,000-gallon tank. If the perc test is 30 min/inch, the drainfield needs more trench length than it would in fast-draining sandy soil at 10 min/inch.
Related calculators
For the building's interior loads, use the drainage pipe sizing and fixture unit calculators.
Septic sizing FAQ
How is the tank size determined?
Tank size is based on the number of bedrooms, which serves as a proxy for daily wastewater flow. Most jurisdictions set a minimum tank size per bedroom count.
What is a percolation rate?
The perc rate, in minutes per inch, measures how fast water drains through the soil. Slower soils need a larger drainfield to absorb the same flow.
Are local rules different?
Yes — health departments vary, so the app gives a sound baseline you should confirm against local requirements before installing.
Does it work offline?
Yes, it runs 100% offline with no account. Free with rewarded ads; a one-time $2.99 Pro unlock adds PDF export and saved history.
Get Septic Sizing on your phone
Free with rewarded ads · $2.99 lifetime Pro · iOS & Android. Works 100% offline on the job site.