What is the standard size of a manhole?
48 inches inside diameter is the common minimum for a sanitary sewer manhole. Texas rules (30 TAC 217.55) say a manhole's inside diameter must be no less than 48 inches, and Illinois (35 Ill. Adm. Code 370.330) sets 48 inches for sewers 36 inches and smaller. Larger pipes need a larger manhole; the agency's standard detail sets the size.
How do you calculate manhole diameter?
Start from the agency minimum, then check that the barrel fits the pipes. Texas requires a diameter that lets personnel and equipment enter and work, and allows proper joining of the pipes in the manhole wall. Illinois adds 48 inches of clearance from an inside drop pipe to the opposite wall. Take the size from the standard detail, then enter it in the manhole volume calculator.
What is the standard size of a manhole cover?
It varies by agency. Texas requires a clear opening of at least 30 inches in diameter where personnel entry is anticipated; Illinois requires an access lid at least 24 inches in diameter. Use the frame and cover named on the project's standard detail.
Sources
Checked 2026-11-02.