If you’re looking for a simple number, it’s usually two-thirds. That’s the "holy majority" we hear about every time white smoke billows over St. Peter’s Square. But when it comes to the Leos—a name shared by thirteen different popes across two millennia—the answer is rarely just a single digit.
Honestly, the math changes depending on which Leo you’re talking about. Are we talking about the Renaissance glitz of Leo X? Or the 19th-century diplomat Leo XIII? Or even the brand-new Pope Leo XIV, who just made history in 2025? The rules that governed how many votes were needed to elect a pope have shifted from "shout the loudest" to complex fractions that would make a high school math teacher sweat.
The 1513 Election: How Leo X Won with 17 Votes
Let’s go back to March 1513. Pope Julius II—the "Warrior Pope"—had just died. Rome was a mess of political maneuvering. When the cardinals locked themselves in for the conclave, there weren't hundreds of them like there are today. There were only 25.
Basically, the rule at the time was the two-thirds majority, a standard set way back in 1179. For the 1513 election, that meant you needed 17 votes to win.
Giovanni de' Medici, who became Pope Leo X, didn't get it on the first try. In fact, on the first ballot, a total underdog named Cardinal Serra i Cau actually pulled 13 votes. People were shocked. It turns out the younger cardinals (the "Young Turks" of the day) were hiding their support for Medici. They didn't want to show their hand too early.
By the second ballot on March 11, the deal was done. Medici secured his 17 votes and became the first of the famous Medici popes. He was only 37. Imagine having the keys to the kingdom before you're even old enough to run for President in the U.S. today.
Why the Number of Votes Changes Every Time
You might think the number of votes is a fixed target. It’s not. It’s a moving goalpost because it depends entirely on how many cardinals actually show up and how many are young enough to vote.
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Since 1970, thanks to Pope Paul VI, if you’re over 80 years old, you’re basically retired from voting. You can hang out, but you don't get a ballot. This means the "two-thirds" threshold is a shifting calculation.
Take a look at how the math worked for the most famous Leos:
- Pope Leo XIII (1878): There were 61 cardinals present. He needed 41 votes to reach the two-thirds mark. He actually crushed it on the third ballot with 44 votes.
- Pope Leo XIV (2025): This was the big one. We had 133 cardinal-electors in the room. To win, the threshold was 89 votes. Cardinal Robert Prevost reached that mark to become the first American pope.
The "Two-Thirds" Rule: More Than Just Math
Why two-thirds? Why not a simple majority of 51%?
Church history is basically a long series of arguments. In the early days, elections were often decided by "acclamation"—essentially a crowd of people in Rome shouting a name until everyone agreed. It was chaotic. Sometimes it led to riots.
In 1179, the Third Council of the Lateran decided that to prevent "antipopes" (rivals claiming the throne), you needed a supermajority. If two-thirds of the guys in the room agree, it's a lot harder for the loser to claim the election was a sham.
The Weird Case of Voting for Yourself
For a long time, there was a tiny, nagging problem: Could a cardinal vote for himself to hit that two-thirds mark?
Technically, yes, for a few centuries. But it was considered incredibly tacky. To fix this, they used to have a weird system where they’d check the handwriting on the winning vote to make sure the guy didn't elect himself. Eventually, Pope Gregory XV got tired of the drama in 1621 and standardized the secret ballot. Now, the rule is a straight two-thirds of the electors present, and nobody cares if you tick your own name as long as the total hits the number.
The 2025 Reality: 89 is the Magic Number
If you were watching the news in May 2025, you saw this play out in real-time. Because Pope Francis had expanded the College of Cardinals significantly, the 2025 conclave was the largest ever.
With 133 electors, the calculation was:
$$133 \times \frac{2}{3} = 88.66$$
Since you can't have two-thirds of a cardinal, you round up. That’s how we got the requirement of 89 votes.
It actually took a few rounds. On the first day, they didn't get there. The black smoke (the fumata nera) told the world that nobody had hit 89 yet. It wasn't until the next day that the 267th pope was chosen.
What Most People Get Wrong About the Count
A lot of people think the voting just keeps going forever. Sorta, but not quite.
John Paul II actually changed the rules in 1996 to allow for a simple majority if the cardinals got stuck for more than two weeks. But then Pope Benedict XVI switched it back in 2007. He felt that a pope needs that big two-thirds mandate to actually lead effectively.
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So, as it stands today—and as it was for Leo XIV—it’s two-thirds or nothing.
Actionable Insights for Church History Buffs
If you’re trying to track the next election or just want to win a trivia night, keep these three things in mind:
- Check the "Sede Vacante" Count: The moment a pope dies, the Vatican releases the list of eligible electors (those under 80). Take that number, multiply by 0.66, and round up. That's your magic number.
- The "Accessus" is Dead: In the old days (like during Leo X's time), cardinals could change their vote after the ballot was read to join the winning side. That's gone. Now, every ballot is a fresh start.
- Smoke Signals Matter: If you see black smoke, it doesn't mean "no one voted." It just means no one hit that specific mathematical threshold.
Understanding how many votes it takes to elect a Pope Leo—or any pope—is really about understanding the Church’s obsession with unity. They don't want a "red state vs. blue state" 51% split. They want a landslide, every single time.
Next Steps for Research:
If you want to see the math in action, look up the "Apostolic Constitution Universi Dominici Gregis." It’s the literal rulebook for the modern conclave. You can also check the official Vatican website during a Sede Vacante (the period when the seat is vacant) for the exact count of electors, which will give you the precise vote requirement for the next election.