Sizing a Septic Tank: Bedrooms, Flow, and Compartments
"Sizing a Septic Tank: Bedrooms, Flow, and Compartments" is lesson 1 of 6 in the Sanitation System (C-42) Learning Hub. It opens with "Two Routes to the Tank Size" and works through 5 short steps, then a worked example you can check yourself against.
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Steps in this lesson
Two Routes to the Tank Size
Dwellings: Table H 201.1(1)
Everything Else: Flow Rate and the Two Formulas
Compartments Inside the Tank
Check the Tank Against the Soil
The worked example in the course applies this lesson to a realistic job in 5 steps, from "Pick the formula" through "Calculate".
What you'll be able to do
Explain the main idea of "Sizing a Septic Tank: Bedrooms, Flow, and Compartments" in plain language you can use on the exam.
Apply this step with confidence: "Everything Else: Flow Rate and the Two Formulas".
Apply this step with confidence: "Compartments Inside the Tank".
Apply this step with confidence: "Check the Tank Against the Soil".
Test yourself on the worked example and the quick-check quiz inside the classroom.
The diagram for this lesson, exactly as it appears in the Learning Hub.
The first steps of this lesson
Step 1: Two Routes to the Tank Size
Section H 201.1 of the 2025 California Plumbing Code (CPC) Appendix H sets septic tank liquid capacity two ways. For dwellings you go by the number of bedrooms (or apartment units) in Table H 201.1(1). For other buildings you use the estimated waste/sewage flow in Table H 201.1(4) or the number of fixture units from CPC Table 702.1, whichever is greater. Always figure the size before you pick the leaching area, because the leaching area is predicated on the tank capacity (Section H 301.1).
Step 2: Dwellings: Table H 201.1(1)
Table H 201.1(1) gives the minimum tank: 1 or 2 bedrooms = 750 gallons, 3 bedrooms = 1,000 gallons, 4 bedrooms = 1,200 gallons, 5 or 6 bedrooms = 1,500 gallons. The table notes add 150 gallons for each extra bedroom, 250 gallons for each dwelling unit over 10, and 25 gallons for each fixture unit over 100. Note 4 says these sizes already include sludge storage and a domestic food waste disposer, so you add no extra volume for a disposer.
The remaining 3 steps, the worked example and the quiz are in the course. This is a preview. The full lesson, with the step-by-step explanations, a worked example and a quick-check quiz, is inside the classroom.
Independent exam preparation. Contractors Classroom is not affiliated with the Contractors State License Board, and no course can guarantee a passing result.
