Sudoku rules: how to play and how to solve it
Sudoku looks like maths but is really pure logic. You never add or multiply: all it takes is looking carefully at which number may go where.
This guide covers the rules, a few techniques that solve most sudokus and the variants you can play on Online igre. If you want to try straight away, open classic sudoku in another tab.
The rules in three sentences
The grid has 81 cells in nine rows and nine columns, and it is also split into nine 3x3 boxes. Some cells are already filled in. Your task is to place the numbers 1 to 9 so that each appears exactly once in every row, every column and every box.
A good sudoku has one solution and can be solved without guessing. If you have to guess, you have missed a logical step somewhere.
First technique: the only possible number
Look at one empty cell and check which numbers already appear in its row, column and box. If only one number is left unused, it goes in that cell.
This is slow if you apply it at random, so start with cells in rows and columns that are already nearly full.
Second technique: the only possible place
Now turn the question around: instead of which number goes in a cell, ask where in a box a seven, say, can go. If a seven already sits in two rows running through that box, only the third row is left, and often only one cell.
This technique, often called scanning, solves a large share of easy and medium puzzles. Work through all the numbers from 1 to 9 in turn.
Notes for harder puzzles
In harder sudokus, pencil in small notes: every number that could still go in a cell. When a new number appears, erase it from the notes in the same row, column and box.
Notes reveal pairs: if two cells in a row can only hold 4 and 8, those two numbers belong to them and can be erased from the rest of the row. That is the first step toward advanced techniques, but most sudokus fall without them.
Variants for when the classic gets old
Mini sudoku uses a smaller grid and numbers up to 6 or 8, which makes it ideal for beginners and short breaks. Killer sudoku adds coloured cages whose cells must reach a given total, so there is a little arithmetic after all.
Sudoku X also bans repeats on the diagonals, and flower sudoku swaps numbers for pictures, which suits children. For a daily habit there is daily sudoku with a fresh puzzle every day.
Number by number to a full grid
Sudoku asks for patience and order, not a talent for maths. Start with easier puzzles, use the techniques in this guide and do not guess, and you will soon move up to harder levels.
Every sudoku game on the site is free and runs in your browser. Find them in the Brain teasers world, and for other logic puzzles visit Daily challenges.