Septic Tank Sizing Calculator
Size septic tanks and estimate drain field requirements
Dwelling Information
Leave 0 to estimate from bedrooms
Water Usage Factors
Soil Conditions (for drain field)
Septic System Requirements
Minimum Tank Size
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Recommended Size
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Daily Design Flow
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Estimated Occupants
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Retention Time
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Drain Field Area
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Trench Length (2ft wide)
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Important: Final sizing requires soil percolation test and local health department approval.
Tank Size Requirements
Based on typical state codes:
| Bedrooms | Min. Tank (gal) | Daily Flow (GPD) |
|---|---|---|
| 1-2 | 750-1,000 | 150-300 |
| 3 | 1,000 | 300-450 |
| 4 | 1,250 | 400-600 |
| 5 | 1,500 | 500-750 |
| 6 | 1,750 | 600-900 |
Soil Loading Rates
| Soil Type | Perc Rate (min/in) | Loading (GPD/sq ft) |
|---|---|---|
| Gravel/Sand | 1-5 | 1.2 |
| Fine Sand | 6-15 | 0.8 |
| Sandy Loam | 16-30 | 0.6 |
| Clay Loam | 31-60 | 0.4 |
| Clay | 60+ | 0.2 |
Septic System Components
Septic Tank
Primary treatment
Solids settle, scum floats
24-48 hr retention
Distribution Box
Flow distribution
Equal flow to trenches
Level installation critical
Drain Field
Final treatment
Soil absorption
Bacterial breakdown
Pump Chamber
If required
For elevated fields
Pressure distribution