How many years of famine?
Gad told David that God was giving him three punishment choices for having the census that he
(or Satan) inspired him to have (See
#212). Two of the choices were the same in the 2 Samuel and 1 Chronicles accounts, but they disagreed on the first option -- famine. The former said seven years, the latter, three.
Seven years of famine
So Gad came to David and told him, Shall seven years of
famine come unto thee in thy land? 2 Samuel 24:13
Three years of famine
So Gad came to David and said unto him, Thus saith the Lord,
choose thee either three years of famine. 1 Chronicles 21:11-12