How to Play Connect Four: Rules, Diagonal Wins and Ties

To play Connect Four, two players take turns dropping discs of their color into one of the 7 columns of an upright grid that is 6 rows high. Each disc falls to the lowest empty spot in its column, and the first player to line up four discs in a row, across, up and down, or diagonally, wins. If all 42 spots fill up and nobody has four, the game is a tie.

These are the rules exactly as Poozee's Four in a Row plays them. Every diagram below was replayed with the game's own engine, and every number comes from code: from listing every possible opening, or from 1,000-game matches between copies of our computer player. (Connect Four is a Hasbro trademark. Poozee's Four in a Row is our own version of the classic game, and we aren't affiliated with Hasbro.) For tactics, read how to win Connect Four.

Connect Four rules at a glance

In this guide, columns are numbered 1 to 7 from the left and rows 1 to 6 from the bottom.

Setting up and the first move

The board starts empty, and each player takes one color. Players alternate, so the first player drops the 1st, 3rd, 5th and every other odd-numbered disc, and the second player drops the even-numbered ones, including the 42nd and last.

Who goes first? Nothing in the rules decides it. Victor Allis points this out in his 1988 thesis on Connect Four (section 1.1): there is no rule saying which color should start. So pick any fair way, such as a coin toss, and then take turns going first, because the first move is worth a lot (see below). On Poozee, red goes first in the first game and the first move switches with every new game, against the computer and in 2 Players mode. Against the computer you are always red.

The first player has 7 choices, but a move and its mirror image (column 1 and column 7, say) lead to the same game reflected, so there are only 4 really different first moves: the middle, or one, two or three columns away from it. From there the number of positions grows quickly, though more slowly than the number of move orders, because the same discs dropped in a different order make the same board:

We counted these by playing out every move order with the game engine.

Taking a turn

On your turn, drop one disc into any column that has room. It falls straight down to the lowest empty spot, so you choose the column, never the row. A column holds 6 discs, and once it is full, nobody can play there again.

There's no passing and no moving discs once they're in, and you never run out of moves: until the board is full, at least one column always has room. On Poozee, click or tap a column, or press a number key from 1 to 7.

How to win: four in a row

You win the moment one of your discs completes four in a row: four of your discs side by side in a straight line with no gaps. The line can run in any of four directions:

• Across (horizontal), in any row.
• Up and down (vertical), in any column.
• Diagonally up to the right, or diagonally down to the right.

Counting every line of four on the board gives 69 possible winning lines: 24 across, 21 up and down, and 24 diagonal. They aren't spread evenly. A disc in the middle column on row 3 or 4 is part of 13 of them, and a disc in a corner is part of just 3, which is one reason the middle column is the best place to start. The strategy guide has the full table.

Five in a row counts too

Four is the minimum, not an exact number. If your disc fills a gap between your own discs, it can make a line of five or more, and that wins just the same.

On Poozee the whole line lights up when the game ends. In our 1,000 Easy games, 21 of the winning lines were five or more long.

Can you win diagonally?

Yes, in both directions, and diagonals are where most players lose track. This game between two of our Medium computers was decided by one:

Red's last disc landed in the middle of the line, between discs played many moves apart, which is exactly why diagonals are easy to miss. Of the 979 games our Medium computers won outright, 312 were won on a diagonal, 667 across, and none up and down. A vertical three is the easiest threat to stop, because the only spot that completes it sits right on top and anyone looking one move ahead blocks it. Between two Easy computers, which only block half the time, 252 of the 996 wins came up and down.

The fastest possible win

A win takes at least 7 discs: the first player's four, plus the second player's three in between. That only happens when the second player never blocks. Of the 823,536 ways to play the first seven discs, 13,032 end with the first player's fourth disc completing a line. The second player's earliest possible win is on the 8th disc, and 44,430 eight-disc move orders end that way.

It happens in casual play: 60 of our 1,000 Easy games were over after 7 discs. The shortest of the 1,000 Medium games lasted 19.

Can Connect Four end in a tie?

Yes. If all 42 spots are full and neither player has four in a row, the game is a tie (a draw). On Poozee the game says "It's a draw: the board is full." and adds one to the Draws count.

Ties are rare. Only 21 of our 1,000 Medium games and 4 of the 1,000 Easy games ended in one.

A full board isn't automatically a tie, though. The game checks for four in a row first, so the 42nd disc can still win, and it always belongs to the second player:

That's how most full boards ended in our Medium games: 65 of the 1,000 games filled the board, and 44 of them were won by yellow with the very last disc.

With perfect play, the game never ends in a tie. Allis showed that the first player can always win by starting in the middle column, and only with that first move (chapter 13 of the thesis). So a tie means the first player let a forced win slip somewhere along the way.

Does going first matter?

Yes. Here is how 1,000-game matches between two copies of our computer player turned out. The last column is the average length of a game, and every game is seeded, so the same games replay exactly:

Easy takes a win most of the time, blocks a threat half the time, and otherwise drops at random with a lean toward the middle. Medium never misses a win or a block and searches four discs ahead. It always opens in the middle and only varies when two moves score the same, so its 1,000 games contain 228 different ones. Between the levels there was no contest: Medium beat Easy in all 1,000 games when it moved first, and in 999 of 1,000 when it moved second.

Every one of the 44 Medium games won by the second player was decided by the 42nd disc. Late in the game, the order in which the last columns fill up decides who has to give way, and our strategy guide explains how odd and even threats settle it, and how to play each side. Our guide to going second traces how those 44 games were decided.

Pro tip: Because the first move is such an advantage, always alternate who starts when you play a friend. Poozee does it for you: each new game switches the first player.

Playing on Poozee

• vs Computer: choose Easy, Medium or Hard. You're red, and who goes first switches every game. 2 Players lets two people share one screen as red and yellow.
• To drop a disc, tap or click a column, or press 1 to 7. With a keyboard, Tab to the board, move between columns with the arrow keys and press Enter.
• Hint shows the column the Hard computer would pick for you, and Undo takes back your last move along with the computer's reply. The score counts wins and draws for each level, and your game is saved in this browser.

Keep playing

• Play Four in a Row against the computer or a friend
• How to win Connect Four: the middle column, double threats and odd and even rows
• How to win tic-tac-toe, the three-in-a-row game where perfect play always ties
• How to play checkers, another rules guide checked with the game's engine