Ultimate tic-tac-toe is tic-tac-toe played on nine boards at once. A big 3×3 grid holds nine small tic-tac-toe boards, 81 squares in all. Two players, X and O, take turns placing one mark at a time. You win a small board with three in a row inside it, and you win the game with three small boards in a row on the big grid. What turns this into a real strategy game is the send rule: the square you choose tells your opponent which small board they must play in next. This guide explains every rule, shows the important situations in diagrams, lists the common house rules, and says exactly which version you play on this site.
Watch: how to play Ultimate Tic-Tac-Toe
How to Play Ultimate Tic-Tac-Toe: Rules Explained Simply
Chapters
Ultimate tic-tac-toe at a glance
- Players: 2, X and O. X always moves first.
- Board: nine small 3×3 boards arranged in a 3×3 grid.
- On your turn: place one mark in an empty square of the small board you were sent to.
- Send rule: your square’s position inside its board picks the board your opponent plays in next.
- Free move: if you are sent to a board that is won or full, play in any open board.
- Small board: three in a row wins it; full with no line is a draw.
- Goal: three won small boards in a row, across, down or diagonally.
- Draw: no moves left and no line of boards.
How to Play Ultimate Tic-Tac-Toe (Rules)
The goal
Your aim is to win three small boards that form a straight line on the big board: a row, a column or one of the two diagonals. It is the same idea as ordinary tic-tac-toe, except that each “square” of the big board is itself a game you must win first.
The board
Think of the big board as an ordinary tic-tac-toe grid whose nine cells each contain a smaller grid. The small boards and the squares inside them are named the same way: top left, top middle, top right, middle left, center, middle right, bottom left, bottom middle and bottom right. So “the top right square of the center board” means the top right square inside the middle small board. This naming is the key to the send rule.
The first move
X moves first and may place a mark in any of the 81 squares. Many players start in the center board, but any square is legal. From the second move on, the send rule decides where each player may play.
The send rule
After each move, look at where inside its small board the square sits. Your opponent must play their next mark in the small board in the same position of the big grid. Play the bottom left square of any small board, and your opponent must play in the bottom left board. Play a center square, and they must play in the center board, even if that is the board you just played in.
This is why ultimate tic-tac-toe takes planning. A square that looks good where you are might send your opponent to a board where they can win, so every move has two sides: what it does for you, and where it sends the other player.
Free moves: when the target board is won or full
Sometimes the send rule points at a small board that is already finished, either won by someone or completely full. Then the player to move gets a free move: they may place their mark in any empty square of any small board that is still open. Finished boards stay closed, so the free move never lets anyone play inside a won or full board.
Free moves are powerful, because the player can go wherever they like, including a board where they have two in a row. Good players avoid sending their opponent to a finished board unless every other choice is worse.
Winning a small board
Three of your marks in a row inside a small board, across, down or diagonally, win that board. The board now belongs to you: on this site a big X or O covers it, and nobody may play in it again, even if some of its squares are still empty.
Drawn small boards
If a small board fills up with no three in a row, it is a drawn board. It belongs to nobody. A drawn board can never be part of a winning line for either player, so it works like a wall on the big board.
How to win the game
The first player to win three small boards in a row on the big grid wins the game at once. The line can run across, down or diagonally, exactly like ordinary tic-tac-toe. Boards won elsewhere don’t matter, and neither does the total number of squares or boards each player holds.
Draws
If every small board is either won or drawn and neither player has a line of three boards, nobody can move and the game ends in a draw. Drawn small boards make this more likely, because they block lines on the big board for both players.
Rule variants and house rules
Ultimate tic-tac-toe has no single official rulebook, so groups play slightly different versions. The most common differences are these.
Won boards stay open
In this variant a won small board is not closed. If you are sent there, you must still play in it, and your mark just doesn’t change who owns the board. Only a full board gives a free move. The game becomes slower and less tactical, since sending someone to a won board is no longer a gift.
Drawn boards count for both players
Some players treat a drawn small board as a wildcard that counts for X and for O. That makes it easier to complete a line of three boards and reduces draws.
Most boards wins
To avoid draws, some groups decide a game with no line of three by counting won small boards: whoever won more boards wins. With equal counts it is still a draw.
Which rules this site uses
- X always moves first, anywhere. Rematch swaps marks so both players get to start.
- The send rule applies to every move after the first.
- A won board is closed, even with empty squares. A full board with no line is a draw board and counts for nobody.
- Sent to a won or full board, you may play in any open board.
- Three won boards in a row win. If no moves remain without such a line, the game is a draw. The “most boards wins” tie-break is not used.
Where the game comes from
Nobody knows for certain who invented the nine-board version of tic-tac-toe. It became widely known after a 2013 blog post by the math teacher and author Ben Orlin, who called it ultimate tic-tac-toe. Since then it has been played in classrooms and used as a programming challenge for game-playing bots, under names such as ultimate, super, strategic and meta tic-tac-toe. The appeal is easy to see: you only need pencil and paper, the rules take a minute to explain, and yet the send rule gives the game real depth.
Common mistakes and rule disputes
- Playing in the wrong board. The board you must play in is set by your opponent’s last square, not by the board they played in. On paper, circle the last move so nobody loses track. On this site the target board is outlined.
- Forgetting the board you just played in. A center square sends the opponent to the center board, so a move can send them right back to where you just played.
- Playing inside a won board on a free move. A free move lets you choose any open board, never a finished one.
- Counting a drawn board. Under the rules used here a drawn board belongs to nobody. If your group plays the “counts for both” house rule, agree on it before the game.
- Ending the game early. A game is not over when one player has won more boards. Only a line of three boards wins; otherwise play continues until no moves are left.
Glossary
- Big board: the 3×3 grid of small boards.
- Small board: one of the nine ordinary tic-tac-toe boards.
- Send rule: the position of your square inside its board picks the board your opponent must play in next.
- Free move: a move in any open board, allowed when you are sent to a won or full board.
- Won (claimed) board: a small board with three in a row; it belongs to that player and is closed.
- Drawn board: a full small board with no line; it counts for nobody.
- Open board: a small board that is neither won nor full.
Play it now
You can play ultimate tic-tac-toe right here with a friend on one device or against the computer on three levels; the board you must play in is always outlined, so the send rule takes care of itself. When you know the rules, read our ultimate tic-tac-toe strategy guide to learn how to use the send rule against your opponent. New to X and O? The tic-tac-toe rules cover the classic one-board game.