Septic Tank Size by Bedrooms

IPC table: 750-1500 gal by bedroom count. State codes vary.

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How to use this calculator

  • Enter bedrooms.
  • Toggle garbage disposal.
  • Verify with local building dept.

About this calculator

IPC standard septic tank sizing by bedroom count: 1-2 BR = 750 gal, 3 BR = 1000 gal, 4 BR = 1250, 5-6 BR = 1500. State codes may require larger. Garbage disposal adds 250 gal (more solids). Tank size determines retention time (typically 24-48 hours) — longer = more solid settling, less burden on drain field. Pump every 3-5 years (don't skip — saves drain field).

Frequently asked

Why bedrooms not occupants?+
Bedrooms = max possible occupancy. State sizing is conservative for resale (next family may have more people).
Garbage disposal effect?+
Doubles solid load. Many septic specialists recommend against on septic systems. Some codes ban.
Drain field?+
Soil percolates effluent from tank. Sized by perc test (water absorption rate). Typically 100-200 ft trenches.
Pumping schedule?+
Every 3-5 years. Inspect annually. Skipping = solids overflow into drain field, $20-50k repair.
Aerobic vs. anaerobic?+
Anaerobic (standard): bacteria break down without O2. Aerobic (advanced): air pumped in, smaller drain field, costs 2-3× more.

Related calculators

Drain Pipe Slope
Slope (in per ft) × run length = total drop. Standard ¼" per ft.
Pipe Diameter for Flow
D = 2 × √(GPM / (velocity × π × 144 × 7.481 / 60)). Find pipe size to deliver target GPM.
Water Pressure (Head Height to PSI)
PSI = ft of head × 0.433. Or 1 PSI = 2.31 ft of water column.
Water Heater Recovery Rate
GPH = (BTU/hr × efficiency) / (8.33 × ΔT). Hot water output rate.
Pump Horsepower for Flow
HP = (GPM × ft head) / (3960 × pump efficiency).
Pressure psi ↔ bar
1 bar = 14.5038 psi = 100 kPa = 0.987 atm.

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