How to seed a bracket
Seeding exists so the two best teams meet in the final rather than in round one. The standard layout puts seed 1 at the top of the draw and seed 2 at the bottom, then fills in so that every round pairs the highest remaining seed against the lowest.
The standard positions
In an eight-team bracket the first-round pairings are 1 v 8, 4 v 5, 3 v 6, 2 v 7 — in that order down the sheet. Seeds 1 and 2 are in opposite halves, 1 and 4 in opposite quarters, and so on.
The property this produces: assuming no upsets, the quarter-finals are 1v8, 2v7, 3v6, 4v5; the semi-finals are 1v4 and 2v3; and the final is 1v2. Every round is the best remaining against the worst remaining.
Where byes go
A bracket holds a power of two and entry lists rarely are one. The difference is made up with byes, and they go to the top seeds — seed 1 first, then 2, then 3.
This is not just convention. It is the only placement that does not distort the draw: a bye handed to a random position gives a free round to whoever happened to be next to it, which is a bigger advantage than any seeding decision you might make elsewhere.
So twelve teams in a bracket of sixteen means the top four seeds skip round one, and the other eight play for the right to meet them.
Seeding from a group stage
When the bracket is fed by groups, the seeding is already decided: group winners are seeded above runners-up, and the layout puts winners against runners-up from different groups.
The thing to get right is that two teams from the same group should not meet again in the first knockout round — they have just played each other. The standard cross-pairing (winner of A against runner-up of B, winner of B against runner-up of A) handles this for an even number of groups.
It breaks down when the bracket is topped up with the best third-placed teams, because which groups those come from is not known until the groups have been played, and the bracket is drawn before that. Competitions that care about this — the Euros, for one — solve it with a published table of every possible combination.
When not to seed
When you have no basis for it. Seeding from a guess is worse than a random draw, because it looks authoritative and it is not. If it is the first time these teams have met, draw at random and say so.
Common questions
What are the first-round pairings for 16 teams?
1v16, 8v9, 5v12, 4v13, 3v14, 6v11, 7v10, 2v15 — which puts 1 and 2 in opposite halves and pairs the best remaining against the worst remaining in every round.
Who gets the byes?
The top seeds, in order. It is the only placement that does not hand a free round to an arbitrary team.
Should I seed a fun tournament?
Usually not. A random draw is fairer than a seeding nobody can justify, and it avoids the conversation about why somebody was seeded where they were.