How long should a flag be flown at half staff when the president the president of the US dies?

On March 1, 1954, President Eisenhower issued a proclamation for the proper ceremonial use of the flag. The United States Veteran's Administration notes the following rules that pertain to high ranking public figures. The sitting President has the right to order the flag flown at half-staff to commemorate the death of other important figures.

"The flag should fly at half-staff for 30 days at all federal buildings, grounds, and naval vessels throughout the United States and its territories and possessions after the death of the president or a former president. It is to fly 10 days at half-staff after the death of the vice president, the chief justice or a retired chief justice of the United States Supreme Court, or the speaker of the House of Representatives. For an associate justice of the Supreme Court, a member of the Cabinet, a former vice president, the president pro tempore of the Senate, the majority leader of the Senate, the minority leader of the Senate, the majority leader of the House of Representatives, or the minority leader of the House of Representatives the flag is to be displayed at half-staff from the day of death until interment."

These rules only apply to the federal government; however, it appears most states have adopted the sames practices.