The Vatican spokesman, the Rev. Federico Lombardi, said Benedict himself had made the decision in consultation with others.
Benedict decided he would be called "Your Holiness Benedict XVI" and either emeritus pope or emeritus Roman pontiff, Lombardi said.
While he will no longer wear his trademark red shoes, Benedict has taken a liking to a pair of hand-crafted brown loafers made for him by artisans in Leon, Mexico, and presented to him during his 2012 visit. He will wear those in retirement, Lombardi said.
Lombardi also elaborated on the College of Cardinals meetings that will take place after the papacy becomes vacant — crucial gatherings in which cardinals will discuss the problems facing the church and set a date for the start of the conclave to elect Benedict's successor.
The first meeting isn't now expected until March 4, Lombardi said, since the official convocation to cardinals to come to Rome will only go out on March 1 — the first day of what's known as the "sede vacante," or the vacancy between papacies.
In all 115 cardinals under the age of 80 are expected in Rome for the conclave to vote on who should become the next pope; 2 other eligible cardinals have already said they are not coming, one from Britain and another from Indonesia. Cardinals who are 80 and older can join the College meetings but are not part of the conclave and can't vote.
Benedict on Monday gave the cardinals the go-ahead to move up the start date of the conclave — tossing out the traditional 15-day waiting period. But the cardinals won't actually set a date for the conclave until they begin meeting officially on March 4.
Lombardi also further described Benedict's final 48 hours as pope: On Tuesday, he was packing, arranging for documents to be sent to the various archives at the Vatican and separating out the personal papers he will take with him into retirement.
On Wednesday, Benedict will hold his final public general audience in St. Peter's Square at which 50,000 tickets have already been requested. He won't greet visiting prelates or VIPs as he normally does at the end but will greet some visiting political leaders — from San Marino, Andorra and his native Bavaria — privately afterwards.
On Thursday, the pope meets with his cardinals in the morning and then flies by helicopter at 5 p.m. to Castel Gandolfo, the papal residence south of Rome. He will greet parishioners there from the palazzo's loggia (balcony) — his final public act as pope.
And at 8 p.m., the exact time at which his retirement becomes official, the Swiss Guards standing outside the doors of the palazzo at Castel Gandolfo will go inside, their service protecting the head of the Catholic Church now finished.
Benedict's personal security will be assured by Vatican police, Lombardi said.