Septic Tank Size Calculator
Free calculator to determine the right septic tank size for your home. Calculate by number of bedrooms, occupants, or tank dimensions. Get capacity in gallons and liters.
Quick Sizing Formula
Daily Flow = Bedrooms × 150 gal/day (or People × 75 gal/day)
Min Tank Size = Daily Flow × 2 (for proper settling time)
🏠 Home Details
Note: Most jurisdictions require a minimum of 1,000 gallons regardless of home size. Always check local codes.
📊 Results
Recommended Tank Size
1,000 gal
3,785 liters
📋 Calculation Details
📊 Septic Tank Size Guide
| Bedrooms | Min. Tank Size | Daily Flow | Max Occupants |
|---|---|---|---|
| 1 Bedroom | 750 - 1,000 gal | 150 gal/day | 2 people |
| 2 Bedrooms | 750 - 1,000 gal | 300 gal/day | 4 people |
| 3 Bedrooms | 1,000 - 1,250 gal | 450 gal/day | 6 people |
| 4 Bedrooms | 1,200 - 1,500 gal | 600 gal/day | 8 people |
| 5 Bedrooms | 1,500 - 1,750 gal | 750 gal/day | 10 people |
| 6 Bedrooms | 1,750 - 2,000 gal | 900 gal/day | 12 people |
* Based on 150 gallons/day per bedroom and 2× daily flow for tank sizing. Add 50% for garbage disposals.
📐 Standard Tank Dimensions
| Capacity | Length | Width | Height |
|---|---|---|---|
| 750 gal | 92" | 60" | 51" |
| 1,000 gal | 127" | 60" | 51" |
| 1,250 gal | 157" | 60" | 51" |
| 1,500 gal | 157" | 69" | 51" |
| 1,750 gal | 180" | 69" | 55" |
| 2,000 gal | 200" | 72" | 58" |
* Dimensions are for low-profile concrete/plastic septic tanks. Actual dimensions vary by manufacturer.
🚽 Understanding Septic Tank Sizing
A properly sized septic tank is crucial for effective wastewater treatment. The tank must be large enough to hold waste long enough for solids to settle (typically 24-48 hours) before liquid effluent flows to the drain field.
Why Bedrooms, Not Bathrooms?
Health departments use bedrooms to calculate potential occupancy: 2 people per bedroom × 75 gallons/day = 150 gallons per bedroom. This ensures the system can handle maximum capacity even if the home is sold to a larger family.
Factors That Increase Size
Garbage disposals add 50% more solids. High-flow fixtures like Jacuzzis, multiple showers, or large washing machines increase daily flow. Water softeners that backwash into the septic also require larger tanks.
Local Codes Matter
Most U.S. jurisdictions require a minimum 1,000-gallon tank regardless of home size. Always check with your local health department before installing. A percolation test determines drain field requirements based on soil absorption rate.
💡 Quick Facts
✓ 150 gal/day per bedroom
✓ 75 gal/day per person
✓ Tank = 2× daily flow
✓ Pump every 3-5 years
✓ 1,000 gal minimum (most areas)
⚠️ Important
An undersized tank causes backups, odors, and drain field failure. When in doubt, go one size larger. The extra cost is minimal compared to repairs.
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Frequently Asked Questions
The most common method is based on the number of bedrooms: multiply bedrooms by 150 gallons per day to get daily flow, then double it for minimum tank size. For example, a 3-bedroom home uses 450 gallons/day, so you need at least a 900-gallon tank (typically rounded up to 1,000 gallons). Most jurisdictions require a minimum of 1,000 gallons regardless of home size. Also consider garbage disposals (+50% capacity), high-flow fixtures, and local codes.
A 2,000-gallon septic tank can typically support 5-6 bedrooms or up to 10-12 occupants. It can handle approximately 1,000 gallons of daily wastewater flow. This size is common for larger homes, multi-family properties, or homes with high water usage. Having a larger tank than minimum required means less frequent pumping (every 4-5 years instead of 3 years).
A leach field (drain field) for a 3-bedroom house typically requires 450-600 square feet of trench area, depending on soil percolation rate. Sandy soils with fast drainage need smaller fields (300-400 sq ft), while clay soils may need 600-900 sq ft. The total area including setbacks and reserve space is usually 4,000-6,000 square feet. A percolation test determines your specific requirements.
A 1,000-gallon septic tank can handle approximately 450-500 gallons of wastewater per day. This is based on the principle that tanks should hold at least 2 days' worth of flow for proper solids settling. A 1,000-gallon tank is suitable for a 3-bedroom home with average water usage. Higher usage from garbage disposals or water-intensive appliances may require a larger tank.
Yes, garbage disposals significantly increase the solids load in your septic tank—typically by 50%. Many jurisdictions require increasing tank capacity by at least 50% when a garbage disposal is installed. For example, if a 3-bedroom home normally needs 1,000 gallons, adding a garbage disposal may require 1,500 gallons. Disposals also mean more frequent pumping (every 2-3 years instead of 3-5 years).
In most U.S. jurisdictions, the minimum septic tank size for new installations is 1,000 gallons, regardless of home size. Some areas allow 750 gallons for 1-2 bedroom homes. Always check with your local health department, as requirements vary by state and county. The minimum is designed to ensure adequate treatment time and reduce pumping frequency.
🚽 Disclaimer: This calculator provides estimates for planning purposes only. Septic system requirements vary by location. Always consult your local health department and obtain proper permits before installing a septic system. A licensed professional should design your system.