How single elimination works
Entrants are paired in a bracket. Each game has a winner, who moves on, and a loser, who is out. The field halves every round until two remain for the final. Because each game removes exactly one entrant and everyone but the champion must be removed, the number of games is always the field minus one.
With 16 entrants that is 15 games over 4 rounds: 8, 4, 2 and 1. The format is fast and easy to follow. Its weakness is that half the field plays only one game, and one bad day ends a strong player's event. The tournament bracket generator builds a seeded single-elimination bracket with byes for 2 to 64 entrants.
How double elimination works
There are two brackets. The winners bracket runs like a single-elimination event, except that a loser drops into the losers bracket instead of going home. A loss in the losers bracket eliminates. The survivor of each bracket meets in the grand final.
The winners bracket finalist has no losses at that point, the losers bracket finalist has one. If the winners bracket side wins the final, the event is over. If the losers bracket side wins, both have one loss, and a second final, called the bracket reset or the if game, decides it. Some organizers play only one final; then the event is not fully double elimination, because the winners bracket side can go out after a single loss. Say in advance which rule you use.
The count follows from the losses. Everyone except the champion loses exactly twice, so that is 2 × (n − 1) losses. The champion adds one more loss only if they came through the losers bracket and the reset is played. Every game produces exactly one loss, so the games equal the losses. Every entrant plays at least two games.
Game counts side by side
The round robin column counts one game for every pair of entrants, n × (n − 1) ÷ 2.
| Entrants | Single | Rounds | Double | Round robin |
|---|---|---|---|---|
| 4 | 3 | 2 | 6 or 7 | 6 |
| 6 | 5 | 3 | 10 or 11 | 15 |
| 8 | 7 | 3 | 14 or 15 | 28 |
| 10 | 9 | 4 | 18 or 19 | 45 |
| 12 | 11 | 4 | 22 or 23 | 66 |
| 16 | 15 | 4 | 30 or 31 | 120 |
| 24 | 23 | 5 | 46 or 47 | 276 |
| 32 | 31 | 5 | 62 or 63 | 496 |
| 64 | 63 | 6 | 126 or 127 | 2016 |
Double elimination costs about twice the games of single elimination at every size. A round robin for 16 entrants needs 120 games, against 15 for single elimination, which is why round robins are kept to small groups or pools. Plan for the higher double-elimination number, because you only know at the final whether the reset is needed.
Byes: filling the bracket
A bracket only halves cleanly when the field is a power of two: 4, 8, 16, 32 or 64. Any other field is rounded up to the next one, and the empty slots become byes, which means a free pass into round two. The number of real first-round games is the field minus half the bracket size.
| Entrants | Bracket | Byes | Round-one games | Rounds |
|---|---|---|---|---|
| 5 | 8 | 3 | 1 | 3 |
| 6 | 8 | 2 | 2 | 3 |
| 7 | 8 | 1 | 3 | 3 |
| 8 | 8 | 0 | 4 | 3 |
| 9 | 16 | 7 | 1 | 4 |
| 10 | 16 | 6 | 2 | 4 |
| 11 | 16 | 5 | 3 | 4 |
| 12 | 16 | 4 | 4 | 4 |
| 13 | 16 | 3 | 5 | 4 |
| 14 | 16 | 2 | 6 | 4 |
| 15 | 16 | 1 | 7 | 4 |
| 16 | 16 | 0 | 8 | 4 |
| 17 | 32 | 15 | 1 | 5 |
| 18 | 32 | 14 | 2 | 5 |
| 19 | 32 | 13 | 3 | 5 |
| 20 | 32 | 12 | 4 | 5 |
| 21 | 32 | 11 | 5 | 5 |
| 22 | 32 | 10 | 6 | 5 |
| 23 | 32 | 9 | 7 | 5 |
| 24 | 32 | 8 | 8 | 5 |
| 25 | 32 | 7 | 9 | 5 |
| 26 | 32 | 6 | 10 | 5 |
| 27 | 32 | 5 | 11 | 5 |
| 28 | 32 | 4 | 12 | 5 |
| 29 | 32 | 3 | 13 | 5 |
| 30 | 32 | 2 | 14 | 5 |
| 31 | 32 | 1 | 15 | 5 |
| 32 | 32 | 0 | 16 | 5 |
Fields just above a power of two are the awkward ones. 17 entrants need a 32-slot bracket with 15 byes and a single round-one game, so one round of the day is spent on two players. If you control the sign-up, aim for 8, 16 or 32, or just below them.
Seeding: who plays whom
Seeding ranks the entrants before the draw, by last season's results, a rating or a qualifier. Standard seeding pairs the highest seed with the lowest, the second highest with the second lowest, and so on. In a bracket of p slots, seed s meets seed p + 1 − s in round one. For 16 entrants:
| Game | Seeds |
|---|---|
| 1 | 1 vs 16 |
| 2 | 8 vs 9 |
| 3 | 4 vs 13 |
| 4 | 5 vs 12 |
| 5 | 2 vs 15 |
| 6 | 7 vs 10 |
| 7 | 3 vs 14 |
| 8 | 6 vs 11 |
The order of the games matters too. Laid out top to bottom as above, seeds 1 and 2 sit in opposite halves and can only meet in the final, and seeds 1 to 4 sit in different quarters and can only meet from the semifinals on. The 8 vs 9 game is the most even pairing and its winner faces the top seed next.
Byes fall out of the same rule. With 12 entrants in a 16-slot bracket, seeds 13 to 16 do not exist, so their round-one opponents, seeds 1, 2, 3, 4, get the byes. That is the usual reward for a high seed.
Without a ranking, draw at random. The random name picker draws names one at a time to fill the slots in order, and the team generator splits a list of players into even teams first if the event is for teams.
The third option: round robin
In a round robin everyone plays everyone once, and the standings decide the winner. Nobody goes home early and the final table ranks the whole field, not just the top. The cost is the game count: 28 games for 8 entrants, 120 for 16. The usual compromise is pools: split a big field into groups of 4 to 6, play a round robin in each, and send the top one or two of each pool into an elimination bracket. The guide how to make a round robin schedule covers the pairings, rounds and tiebreakers.
Which format to pick
| Situation | Format |
|---|---|
| One evening, many entrants | Single elimination |
| A full day, one loss feels harsh | Double elimination |
| 3 to 8 entrants, everyone should play a lot | Round robin |
| A big field and a full day | Pools, then a bracket |
To estimate the time, multiply the games by the length of one game and divide by the courts, tables or boards you can run at once. 31 double-elimination games of 20 minutes on 4 courts take about 155 minutes of play, plus changeovers. The real limit is the final rounds: the last games run one at a time, so a single court sets the pace at the end.
Checklist before the first game
- Count the entrants and look up the bracket size and byes in the table.
- Decide how seeds are set, or draw at random, and publish the bracket.
- For double elimination, say whether the final can be reset.
- Agree on the rules for a single game: length, tiebreak, who reports the score.
- Track results as you go with the score keeper, so nobody argues about a game an hour later.
Frequently asked questions
How many games does a single-elimination tournament need?
One fewer than the number of entrants. Every game knocks out exactly one player or team, and everyone except the champion has to be knocked out, so 16 entrants need 15 games and 12 entrants need 11. Byes do not change the total, they only change how the games are spread over the rounds.
How many games does a double-elimination tournament need?
Twice the number of entrants minus two, or minus one if the final has to be replayed. Everyone except the champion loses twice, and the champion loses either zero times or once. With 16 entrants that is 30 games, or 31 with the second final.
What is a bracket reset?
The second game of a double-elimination final. The winners bracket finalist arrives with no losses and the losers bracket finalist with one. If the losers bracket side wins the first final, both now have one loss, so a second game decides the title. Some events play a single final instead, which means the winners bracket side can be knocked out after only one loss.
How many byes do I need?
Round the number of entrants up to the next power of two (4, 8, 16, 32, 64) and subtract. Twelve entrants fill a 16-slot bracket with 4 byes, and 20 entrants fill a 32-slot bracket with 12 byes. With standard seeding the byes go to the top seeds.
Which format should I pick?
Single elimination when time or courts are short, because it needs the fewest games. Double elimination when one bad game should not end anyone's day, at the price of roughly twice the games. A round robin when everyone should play everyone, which only works for small groups because the game count grows with the square of the field.
Sources
- Wikipedia: Single-elimination tournament (the loser of each match is eliminated; standard seeding pairs the highest with the lowest seed; the top two seeds cannot meet before the final)
- Wikipedia: Double-elimination tournament (winners and losers brackets; the final is usually two possible games, the second called the if game or bracket reset; one or two games fewer than twice the field; used in NCAA baseball and softball regionals)
- Skedge: Double elimination brackets explained (2N−2 matches with an undefeated champion, 2N−1 when the bracket reset is played)