Septic System Sizing - IRC

Septic sizing calculator. Tank & drain field. IRC code compliant.

Septic System Sizing Calculator helps you calculate septic tank size and drain field area using the tank and absorption-field tables commonly adopted by state health departments and the private sewage disposal codes. Instantly determine required tank size based on occupancy and flow, then calculate drain field area using soil percolation rate. Support 5 soil types with application rates from sandy soil through clay. Works 100% offline on the job site. Useful for septic system design, permitting, and installation.

FEATURES
• Septic Tank Sizing: 1,000 gal through 3 bedrooms, 1,250 gal for 4, 1,500 gal for 5, +250 gal per additional bedroom (150 gal/bedroom/day design flow)
• Daily Flow Estimation: Automatic calculation of design flow using standard residential plumbing fixture loads
• Drain Field Area: application rate by percolation rate (1.2 / 0.8 / 0.6 / 0.4 gal per sq ft per day for 1-5 / 6-15 / 16-30 / 31-60 min per inch); slower than 60 min/in is flagged as not suitable for a standard field
• 5 Soil Presets: gravel/coarse sand, sand, sandy loam, loam, and clay loam with typical percolation rates
• Custom Percolation Rate: Override pre-set rates and enter your site-specific perc test results
• Tank Size Options: Standard tank sizes from 1000-2000+ gallons with recommendations
• System Capacity Verification: Check if existing tank meets IRC minimum requirements

HOW IT WORKS
1. Enter number of bedrooms in the residence
2. View calculated daily design flow and IRC minimum tank size
3. Select soil type from perc test (sandy soil to clay)
4. App calculates required drain field area in square feet
5. Export sizing recommendation to PDF for permit application

PERFECT FOR
• Septic system installers and contractors
• Plumbers designing and installing septic systems
• Home builders sizing systems for new construction
• Plumbing inspectors and health inspectors verifying system compliance
• Plumbing apprentices preparing for master/journeyman exams
• Environmental health specialists and site evaluators
• Soil scientists with perc test data

OPTIONAL PRO UPGRADE — $2.99 ONE-TIME IN-APP PURCHASE
The following features require a separate one-time in-app purchase. They are not required to use the calculator:
• Unlimited saved calculation history
• PDF export of results
• Dark theme
• Ad-free experience

STANDARDS & COMPLIANCE
IRC (International Residential Code) Table P2602.1 Minimum Septic Tank Size Requirements, IRC Table P2602.2 Absorption Field Area Requirements, Standard residential design flow of 150 gal/bedroom/day, Soil percolation rate classifications and application rates per IRC Appendix P.

PERFECT FOR
• Septic system installers and contractors
• Plumbers and drain installers
• Home builders and builders' estimators
• Plumbing and health inspectors
• Site evaluators and engineers
• Environmental health professionals

OFFLINE & PRIVACY
• Works 100% offline - calculate systems anywhere
• No account required - instant access without signup
• No data collection - all designs stored locally
• No internet dependency

Part of PlumbTools Suite - professional plumbing calculator tools for septic system design. Calculate tank and drain field sizes accurately, ensure IRC compliance, and speed up system permitting with accurate septic sizing calculations.