Pairing number in chess tournaments

Pairing number

Definition

A pairing number is the fixed numeric identifier assigned to each participant (player or team) at the start of a tournament. It is used by the pairing system to generate who plays whom and with which colors. In Swiss events it is usually the “start number” or seed (No. 1 = highest-rated), while in round-robin events it determines the exact schedule via predefined tables (often called Berger tables). Pairing numbers remain constant for the duration of the event.

How it is used in chess

• Swiss-system tournaments (see Swiss system):
  • Seeding: Players are ordered by rating (and other tiebreak criteria if needed), and assigned pairing numbers 1, 2, 3, …
  • Round 1 pairings: Commonly, the field is split into top and bottom halves and paired “down the middle,” e.g., 1 vs 9, 2 vs 10, etc., in a 16-player event. Organizers may specify which half gets White in Round 1.
  • Later rounds: Within each score group, players are sorted first by score, then by pairing number. This order helps the algorithm choose pairings, manage color balancing, and determine who may “float” to a neighboring score group.
  • Byes: If there is an odd number of players, the eligible bye recipient is often identified within the lowest relevant score group, with pairing number helping to break ties among otherwise equal candidates (subject to the tournament’s rules and the player not having received a bye already). See Bye.
  • Late entries/withdrawals: If allowed, new players typically receive the next available pairing number; the existing numbers are not changed once published.
• Round-robin tournaments (see Round-robin and Berger table):
  • Pairing numbers determine the entire schedule in advance via a standard table (the “Berger” or “circle” method). Colors are also prescribed by the table or by event settings.
  • At elite round-robins, pairing numbers are often drawn by lot at the opening ceremony instead of being assigned by rating.
  • In double round-robins, the second cycle typically mirrors the first with colors reversed.
• Team events: Teams receive pairing numbers to produce the team-versus-team schedule. Board orders within a team are a separate matter.
• Tie-breaks: While uncommon, some regulations list “starting rank” (related to pairing number) as a final tie-break after performance-based systems like Buchholz or Sonneborn–Berger.

Strategic and practical significance

• Color expectations: The top seeds often receive a favorable first-round color (frequently White), which can influence opening preparation.
• Opponent strength: Early rounds in Swiss events tend to pair higher seeds against lower seeds, impacting risk management and scoring strategy.
• Logistics: Your pairing number appears on player lists and can help you quickly locate yourself in pairing sheets each round. Don’t confuse it with the round’s board number, which changes by round and score group.

Examples

Example A: 16-player Swiss, Round 1

• Players are seeded 1–16 by rating. Round 1 pairs top vs bottom:
  • 1 vs 9, 2 vs 10, 3 vs 11, 4 vs 12, 5 vs 13, 6 vs 14, 7 vs 15, 8 vs 16
• Event regulations specify which half gets White; often 1–8 take White, 9–16 take Black (but this can be inverted by the arbiter).
• If all favorites win, the 1-point score group might list as 1, 2, 3, 4, 5, 6, 7, 8 (by pairing number), which then guides Round 2 pairings and color balancing.

Example B: 8-player Swiss, color and ordering inside score groups

• Seeds and pairing numbers: 1–8.
• Round 1 (top half White): 1–5, 2–6, 3–7, 4–8.
• Suppose 1, 2, 3, 4 win. The 1-point group is ordered as 1, 2, 3, 4 by pairing number; color histories are then considered for Round 2 (e.g., someone who had White may be steered to Black if possible).

Example C: 6-player round-robin (single cycle) using pairing numbers

• Assign pairing numbers by lot or rating: 1–6.
• One common Berger schedule (left player has White by convention; tournament rules may flip colors):
  • Round 1: 1–6, 2–5, 3–4
  • Round 2: 6–4, 5–3, 1–2
  • Round 3: 2–6, 3–1, 4–5
  • Round 4: 6–5, 1–4, 2–3
  • Round 5: 3–6, 4–2, 5–1
• In double round-robins, play the same sequence again with colors reversed.

Historical notes

• Berger tables: Named after Johann Berger, these standardized schedules for round-robins cemented the practice of assigning pairing numbers to drive who-plays-whom and color allocation.
• Swiss codification: Modern FIDE Swiss pairing regulations formalize the use of start numbers for sorting and pairing within score groups, ensuring reproducible results across arbiters and pairing software.

Tips and common pitfalls

• Know your number: Find your pairing number on the published starting list; it won’t change even though your board number will.
• Color assumptions: Don’t assume you’ll always get White (or Black) based on your pairing number—after Round 1, color allocation follows color-history rules, not just seeding.
• Late changes: Once pairing numbers are published, arbiters avoid renumbering; if players join late, they typically receive the next available number.

Interesting facts

• In many elite round-robins (e.g., Candidates Tournaments), players draw pairing numbers at the opening ceremony to generate the entire schedule on the spot.
• The top seed’s pairing number often places them on the broadcast top board in early Swiss rounds, which can subtly influence preparation due to increased visibility.