42 slots, trillions of games
Seven columns and six rows give you just 42 spaces. Those spaces still allow 4,531,985,219,092 legal positions, a count worked out by the computer scientist John Tromp.
Play Connect Four online
Drop Four is a free Connect Four game — also written Connect 4 — that runs in the browser, with nothing to install and no sign-up. Pass the device back and forth for a two-player game, or play the Easy or Hard bot. Take turns dropping a counter into a column, and the first player to line up four — across, upwards or diagonally — wins the game.
Fun facts
The game is solved
In October 1988 James Dow Allen and Victor Allis independently cracked it, weeks apart and without knowing about each other. Allis wrote his version up as a university thesis, and the perfect result has been known ever since.
Always open in the middle
With flawless play from both sides, the first player wins only by starting in the centre column. Opening beside it draws, and opening in the outer columns loses. That is why the Hard bot here quietly adds points for holding the middle.
No game runs past 42 moves
Every move fills exactly one slot and nothing ever comes off the board, so the grid doubles as the clock. A game that reaches move 42 with nobody connecting four is a draw.
The Captain's Mistress
A much repeated story claims a similar game kept Captain James Cook busy on long voyages, and that his crew nicknamed it after the thing stealing his attention. It is a lovely tale, though it belongs to folklore rather than to any documented ship's log.
Boxed since 1974
Milton Bradley put the upright grid and the two colours of disc into shops in 1974, which is when the game turned into a household fixture rather than a curiosity.
How the Hard bot thinks
It looks five moves ahead using minimax, scoring every possible future board, and uses alpha beta pruning to throw away whole branches the moment they cannot beat something it has already found. The same idea drives classical chess engines.
Tic tac toe with gravity
Formally it sits in the family of m,n,k games alongside noughts and crosses and Gomoku. The twist is that you pick a column rather than a square, so gravity chooses your row for you and most of the board is out of reach on any given turn.
The solved games club
Qubic fell in 1980 and Connect Four in 1988. Draughts held out until 2007, after roughly eighteen years of computation by Jonathan Schaeffer's team, and the answer turned out to be a draw with perfect play on both sides.
Zermelo got there in 1913
Long before computers, Ernst Zermelo proved that any finite two player game with no hidden information and no dice has a guaranteed best outcome. Connect Four is simply one of the games that took another 75 years to actually calculate.
Read more
How to play Connect Four
The rules in full: the board, how discs fall, what counts as four in a row, and when a game is a draw.
7 min read
How to win at Connect Four
Why the centre column decides games, how double threats work, and the odd and even row rule.
7 min read
Connect Four was solved twice in one month
Two researchers cracked the perfect result in October 1988, weeks apart, without knowing about each other.
6 min read
A short history of Connect Four
From a sea captain's legend to a 1974 boxed game, and the family of games it belongs to.
5 min read