Swiss pairing calculator

What the Swiss system is

In a Swiss tournament nobody is eliminated. Everyone plays the same fixed number of rounds, and in each round you play someone whose record so far is similar to yours. Win and you meet stronger opposition next round; lose and you meet weaker. After a handful of rounds, the players with the best records have all beaten similarly strong opponents, so the standings are meaningful without playing everyone. Chess events, Magic: The Gathering tournaments and the Swiss stages of several esports championships work this way.

The appeal is efficiency. Sixteen players in a round robin need 120 matches; a Swiss with 4 rounds needs 32, and every player still gets four games instead of being knocked out after one. The cost is complexity: someone has to produce the pairings for every round, avoid rematches, handle the odd player, and break ties. That is the part this calculator does.

How this calculator pairs a round

1. Rank everyone by points, then Buchholz, then the order you entered them.
2. Round 1 pairs the top half of your list against the bottom half: 1 v N/2+1, 2 v N/2+2, and so on. That is why you should enter players strongest first, or use the shuffle button if you have no seeding.
3. Later rounds group players by score. Inside a group the top half plays the bottom half, again in ranking order, so the best player in a group meets someone from the lower half of that group rather than the next-best player.
4. Odd groups send their lowest-ranked player down to be paired with the next score group (a “floater”).
5. No rematches: if the natural pairing would repeat a game, the search backtracks and tries the next best partner, all the way down, and only accepts a repeat when no complete pairing without repeats exists.
6. The bye (odd number of players) goes to the lowest-ranked player who has not had one, and counts as a win.

How many rounds you need

With no draws, the number of players still undefeated is at most halved every round, because undefeated players play each other. After ceil(log2 N) rounds there is at most one undefeated player, which is the standard minimum for declaring an undisputed winner.

More rounds sort out the middle of the table more accurately, but there is a ceiling: each player can only face every other player once, so an event with N players (N even) can run at most N−1 rounds without rematches. The calculator enforces that limit.

Buchholz and the ranking

Points alone leave many ties in a Swiss, because with few rounds many players finish on the same score. Buchholz breaks those ties by strength of schedule: add up the points of every opponent you actually played. Beating people who themselves won a lot is worth more than beating the players who went 0–3. The standings table shows the value so you can check it.

Two honest caveats. Buchholz is unstable in early rounds, when nobody’s record means much yet. And it can be gamed at the margins by a big win streak against a weak group, which is why serious events publish their tiebreak order before the first round. The calculator uses points, then Buchholz, then entry order; if the last of these decides a prize or a qualification spot, run a tiebreak match instead.

Using the calculator

Paste your players, choose the scoring (win/loss only is typical for esports, the other two allow draws), and press Start tournament. Set each board’s result with the drop-down. When the round is complete, thePair next round button unlocks. The standings update as you enter results. You can copy the latest pairings or the standings as text to post in a chat, and the share link stores every pairing and result, so you can close the tab and pick the event up later, or hand it to a co-organizer.

Two safety rules protect your data: you cannot edit a finished round once the next round has been paired from it, because that would invalidate the pairings, and editing the player list does not touch a running event until you press Start again.