About this tool
The septic tank calculator estimates tank capacity and drain field size for residential properties not connected to municipal sewers. Sizing follows EPA and most state health department guidelines based on number of bedrooms, which approximates daily wastewater flow.
How it works
Tank Size = Flow × 1.5 day retention
Leach Field = Daily Flow × Soil Factor
Bedroom count is used as a proxy for occupancy. The tank holds 1.5 days of wastewater for settling. Leach field area scales with both daily flow and soil percolation rate, with clay soils needing larger absorption areas than sand.
How to use the Septic Tank Size Calculator
The Septic Tank Size Calculator is a browser-based tool that runs entirely on your device. Inputs you enter never reach a server - all calculations happen client-side in JavaScript. This means:
- Privacy: nothing is logged, sent, or stored by 3Tej. Inputs disappear when you close the tab.
- Speed: results update as you type. No network round trip.
- Offline use: once the page is cached, it works without internet.
- No signup: no account, no email, no rate limits.
Step by step
- Enter your inputs in the form above. Each field is labeled with its unit (currency, percent, kg, etc.) and the expected range.
- Read the result as it updates. The number reflects the formula commonly accepted in Septic Tank Size-related calculations.
- Adjust to see sensitivity: change one input at a time and watch how the output moves. This is the fastest way to understand which variable matters most.
- Copy or screenshot the result for later reference. The page state persists for the session if your browser allows it.
When you would use this
- Quick estimates: when you need a number now and don't want to open a spreadsheet.
- Sensitivity analysis: testing how a result changes as inputs vary, before committing to a real-world decision.
- Comparison: running the same calculation with different inputs to compare options side by side.
- Learning: building intuition for how the underlying math behaves.
- Documentation: capturing a snapshot of inputs and outputs at a point in time.
Frequently asked questions
How do I size a septic tank?
Septic tanks are sized by bedroom count. Two bedrooms need about 750 gallons, three need 1,000, four need 1,250, and five or more need 1,500 or larger.
How big should the leach field be?
Leach field size depends on soil percolation rate and daily wastewater flow. Typical sizes range from 600 to 2,000 square feet for residential systems.
How often should I pump my septic tank?
Pump the tank every 3 to 5 years for a typical household. Heavy use, garbage disposal use, or smaller tanks may require pumping every 2 to 3 years.
What permits do I need?
Local health departments require permits for new septic systems and major repairs. A licensed installer typically handles permit applications and required inspections.
Is the Septic Tank Size Calculator accurate?
The Septic Tank Size Calculator applies the standard formula for septic tank size. Accuracy is limited only by your input precision. For decisions with material consequences, use the result as a starting point and verify with a qualified professional or the relevant official source.
Is the Septic Tank Size Calculator free?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads that appear around the tool but not inside the calculation flow.
Are my inputs saved?
No. Inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but does not see what you type into the form.
Can I use the Septic Tank Size Calculator on my phone?
Yes. The tool is responsive and tested on iOS Safari, Android Chrome, and major desktop browsers. Touch targets meet Apple's 44pt and Google's 48dp minimum guidance.
How do I report a bug or suggest improvement to the Septic Tank Size Calculator?
Email hi@3tej.com with the URL of this page and a description of what you saw vs expected. We typically respond within 72 hours and update calculators when rules or formulas change.
How accurate is the Septic Tank Size Calculator?
It applies the standard formula. Accuracy is limited only by your input precision. For decisions with material consequences (taxes, medical, legal, structural), use the result as a starting point and verify with a qualified professional in the relevant field.
Is the Septic Tank Size Calculator free to use?
Yes. 100% free, no signup, no payment, no API key. The site is funded by display ads around the tool but not inside the calculation flow.
Are my inputs saved anywhere?
No. All inputs stay in your browser tab. Closing the tab discards them. The site uses Google Analytics for traffic measurement (anonymized) but the analytics never see what you type into the form.
Does the Septic Tank Size Calculator work offline?
Yes. Once the page has loaded, it works without internet. The calculation runs in JavaScript on your device.
Can I share results from the Septic Tank Size Calculator?
Take a screenshot or copy the output. The page doesn't generate shareable URLs for specific calculations - inputs stay in your browser only.
Why are the results different from another septic tank size tool?
Most likely: different formula assumptions, different default values, different rounding rules, or different applicable rates. Check the methodology if both tools document it. Both can be valid for different scenarios.