Septic Tank Size Calculator (Florida Rule 62-6.008: Tank Gallons & Drainfield Area)
Minimum septic tank size, pump tank size and drainfield area for a single-family home under Florida Rule 62-6.008, from bedrooms, building area and soil type.
Formula
Design flow = the larger of the bedroom flow (100 gpd per bedroom up to 4, then +60 per bedroom) and the building-area flow (100 gpd to 750 sq ft, 200 to 1,200, 300 to 2,250, 400 to 3,300, then +60 per extra 750 sq ft or fraction), per Table I and its footnote 4. Septic tank and pump tank minimums come from Table II for that flow. Drainfield area = max(flow, 200 gpd) ÷ the Table III loading rate for the soil and trench or bed.
Worked example
Inputs: Bedrooms = 3; Building area = 2000 sq ft; Soil (from the site evaluation) = slight; Drainfield type = trench.
| Flow by bedrooms gpd | 300 |
|---|---|
| Flow by building area gpd | 300 |
| Design flow gpd | 300 |
| Septic tank min gallons | 900 |
| Pump tank min gallons if used | 225 |
| Loading rate gpd per sq ft | 0.8 |
| Drainfield min sq ft | 375 |
Florida Rule 62-6.008 minimums for one single-family dwelling unit; the larger of the bedroom and building-area flows applies. The permit sets the final size from a site evaluation; multi-unit, commercial and aerobic systems follow other parts of the rule.
FAQ
What size septic tank for a 3 bedroom house in Florida?
For 3 bedrooms and 1,201 to 2,250 sq ft, Table I gives 300 gallons per day, and Table II sets a 900 gallon minimum effective tank capacity. A 4 bedroom home of up to 3,300 sq ft is 400 gpd, which is a 1,050 gallon tank.
Why does house size matter if bedrooms don't change?
The rule says that when bedrooms and building area point to different flows, the larger applies. A 4 bedroom, 3,500 sq ft house is 400 gpd by bedrooms but 460 gpd by area (400 + 60 for the extra 200 sq ft), which moves it to a 1,200 gallon tank.
How big does the drainfield need to be?
Flow divided by the soil's loading rate, using at least 200 gpd. In slightly limited sandy soil a trench takes 0.80 gpd per sq ft, so 300 gpd needs 375 sq ft; an absorption bed (0.60) needs 500 sq ft. Clayey soils need far more.
What is the pump tank number?
If the system needs a pump tank, Table II also sets a minimum pump tank capacity: 225 gallons at 201 to 300 gpd for a residence.
Is this the final size?
No. It is the rule minimum. A Florida onsite sewage permit is based on a site evaluation (soil, water table, setbacks), and the permit can require more. Multi-family, commercial and aerobic units follow other parts of the rule.
Sources
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Last reviewed 2026-10-20.