How to solve Sudoku: a beginner guide

The rules

Fill the grid so that every row, every column and every 3 x 3 box holds each number from 1 to 9 exactly once. A good puzzle has only one solution and never needs guessing.

Method 1: the only place (scanning)

Pick a number and a box. Look along the rows and columns that cross the box: wherever that number already appears, it blocks the whole row or column. If only one square in the box is left open, the number goes there.

In the picture, the 4 must go at row 1, column 9: the circled 4s rule out every other square in the yellow box.

Tip: start with the number that already appears most often in the grid. Scan every box for it, then move on to the next number.

Method 2: the only number

Pick an empty square and list the numbers already in its row, column and box. If eight different numbers are there, the ninth is the answer.

In the picture, the square at row 2, column 7 can only be 5.

Use this method on squares in busy rows and columns: they have the fewest choices.

Pencil notes

For harder puzzles, write the possible numbers small in each empty square (in the PlayZoneMasti game, switch Notes on). Each time you fill a square, rub that number out of the notes in its row, column and box. Our game does this for you.

A square whose notes shrink to one number is solved.

For harder puzzles: pairs and pointing

• Pairs: if two squares in a row, column or box can only be the same two numbers (say 3 and 7), those two numbers belong to those squares. Remove 3 and 7 from the notes of every other square in that row, column or box.
• Pointing: if inside a box a number can only go in one row (or one column), it cannot go anywhere else in that row (or column) outside the box. Remove it from those notes.

Easy and Medium puzzles in our game never need these; Hard and Expert sometimes do.

Tips and common mistakes

• Never guess. If you are stuck, scan every number again; there is always a next step.
• Check all three: before writing a number, check its row, column and box.
• Work number by number at first, then square by square.
• Take breaks: a fresh look often spots the next number at once.

Ready? Play today's free Sudoku.