Septic tank size by state / East North Central
Michigan septic tank size
Michigan has no statewide minimum septic tank size. The tank for a house is set by the county or local health department that issues the permit, so the answer depends on where the house is. This page explains who decides, quotes the state source, and shows what neighbouring states require for comparison.
What the Michigan rule says
The rule is No statewide residential code; single/two-family systems governed by local health department sanitary codes (Public Health Code Act 368 of 1978). Michigan Criteria for Subsurface Sewage Disposal covers other than single/two-family systems up to 10,000 gpd., administered by Local health departments (sanitary codes); Michigan EGLE oversees larger systems. In its own words:
"approvals for wastewater systems serving single and two family dwellings fall under the jurisdiction of LHD sanitary codes." "Of the 44 LHD jurisdictions, 39 operate under their own separate set of regulations for on-site wastewater systems." Michigan Criteria apply to "other than single and two family home systems with flows up to 10,000 gallons per day."
Source: No statewide residential code, read 2026-10-20.
- Michigan has no statewide residential septic code. Each local health department's sanitary code sets the tank size.
- Bills to create a statewide code (SB 299/300) were still in committee at the last check.
How Michigan compares with nearby states
Illinois requires 1,000 gallons for three bedrooms; Indiana requires 1,000 gallons for three bedrooms; Ohio requires 1,500 gallons for three bedrooms.
Before you size a tank in Michigan
- Bedrooms, not people, set the size in most rules. Rooms that could be used as bedrooms are usually counted, so check how your permitting office counts a den or a finished basement.
- Garbage disposals, grinder or ejector pumps and large tubs change the answer in many states; the points above list Michigan's adjustments.
- The tank is only half the system. The drainfield is sized separately from soil tests, and it is usually the bigger cost.
- A private well on the same lot has its own setbacks from the tank and field; the well pump and pressure tank calculators size the water side.
Figures are the state's minimum as written on 2026-10-20. Local health departments can require more; the permit issued for your property governs. See the methodology for how each state was read.