At first glance, sudoku looks like a number puzzle for math whizzes, but nothing could be further from the truth: you don't need to do any math, just think logically. Here you'll read in plain language what sudoku is and how to play it.
Sudoku is a number puzzle that became popular in Japan in the 1980s and is now played all over the world — in newspapers, puzzle books, and online. The idea is simple: you get a grid in which some numbers have already been filled in, and you fill in the rest. There's no arithmetic involved; the digits 1 through 9 are really just nine different symbols. The only thing that counts is logical thinking.
A sudoku consists of a large square of 9 by 9 cells: 81 in total. That large square is divided into nine smaller boxes of 3 by 3 cells. Some cells are already filled in at the start; those fixed numbers are your anchor and cannot be changed.
Fill every empty cell with a digit from 1 through 9, so that every digit appears exactly once in every row (from left to right), exactly once in every column (from top to bottom), and exactly once in every 3-by-3 box. There are no other rules — and every good sudoku has exactly one solution.
Start with the rows, columns, or boxes that already contain many numbers: few possibilities remain there. First look for cells where only one digit can fit; there always are some. Another pleasant approach: pick one digit (the 5, for example) and check which boxes it's still missing from — you can often place it somewhere with certainty. Work calmly and one digit at a time; sudoku is not a race. Want to take the next step afterwards? Then learn the most important sudoku techniques — from naked singles to pencil marks.
The temptation to “just try something” is strong. Don't do it: one guess that turns out wrong often brings down half the grid. Every puzzle on BreinPlezier can be solved with pure logic — there is always a cell somewhere where only one digit fits.
A digit has to be right in the row, the column, and the 3-by-3 box — all three at once. Briefly check all three directions for every digit; that prevents most mistakes.
Don't stare yourself blind at one corner of the grid. If you're stuck, look somewhere else: you'll often find an easy cell there, and after that the rest gets going again by itself.
The longer a mistake stays on the board, the more new numbers build on top of it. In doubt? Use the “Check mistakes” button — wrong cells are calmly marked in red and you can correct them right away.
That's really all you need to know. Start with an easy puzzle — most cells are already filled in there — or join in with today's puzzle right away. Prefer to practice on paper? You can also print our puzzles for free as a PDF.
More questions? Have a look at the frequently asked questions about sudoku, or read why everything on BreinPlezier is completely free.