How to Play Sudoku: The Gentle Introduction
Sudoku is a logic puzzle played on a 9 by 9 grid. Despite all the numbers, it involves no arithmetic whatsoever — you never add, subtract or multiply. The numbers are simply symbols to place by logic.
The grid
The big square is divided into:
- 9 rows running across
- 9 columns running down
- 9 boxes of 3 by 3 squares
Some numbers are printed in advance. These are called givens, and they can never be changed. The more givens a puzzle has, the gentler it is — the puzzles on this site have around 37, which is a comfortable starting level.
The only three rules
1. Every row must contain the numbers 1 to 9, each exactly once. 2. Every column must contain the numbers 1 to 9, each exactly once. 3. Every 3 by 3 box must contain the numbers 1 to 9, each exactly once.
That is the whole game. A finished grid has 81 squares filled with no repeats in any row, column or box.
Placing your first numbers
- Look for a row, column or box that is nearly full. If a row already has eight numbers, the ninth is forced — only one number can be missing.
- Pick a number, say 5, and scan every row and column that already contains a 5. Cross out (mentally) where a 5 cannot go. In many boxes only one square remains — the 5 belongs there.
- Work one number at a time, and re-scan after every placement. Each number you place gives you new information.
Good habits
- Use pencil (or the erase button) freely. Mistakes are part of the process.
- Never guess wildly. In a well-made puzzle every step follows from logic. Our sudokus are computer-checked to have exactly one solution, so if you are stuck, the answer is always deducible from what is on the grid.
- Check as you go. Each time you complete a row, column or box, glance through it for duplicates.
Ready when you are: try a gentle sudoku — big squares, big numbers, no fuss.
