Jamieson, Fausset and Brown on 1 Chronicles 23:3

3. the Levites were numbered ... thirty and eight thousand--Four times their number at the early census taken by Moses (see on Nu 4:1-49; 26:1-51). It was, in all likelihood, this vast increase that suggested and rendered expedient that classification, made in the last year of David's reign, which the present and three subsequent chapters describe.

by their polls, man by man--Women and children were not included.