How to play Sudoku

Fill the empty cells with the numbers 1 to 9. Each row, each column, and each 3 × 3 box must contain every number exactly once.

That is the whole rule set for classic Sudoku. You don’t add the numbers or calculate a total. You use the numbers already on the board to work out which positions are possible.

Know the three parts of the board

A classic board has 81 cells arranged in nine rows and nine columns. Heavier lines divide it into nine boxes. Each box is three cells wide and three cells tall.

A number you place must fit all three groups at once. If its row is clear but its column already contains that number, the placement does not work. The printed clues are fixed and should stay in place.

Start where fewer cells are empty

Find a row, column, or box that is nearly full. List the numbers it is missing. Then check an empty cell against the other two groups it belongs to.

For example, a row containing 1, 2, 3, 4, 5, 6, 7, and 9 is missing 8. If that row has one empty cell, 8 is the only candidate. Confirm that its column and box allow it before writing it in.

Make a first move in the practice puzzle

Open the large print practice puzzle. Count rows from the top and columns from the left. Look at the center cell, in row 5 and column 5.

Row 5 contains 4, 8, 3, and 1. Its missing numbers are 2, 5, 6, 7, and 9.
Column 5 contains 7, 9, 6, 2, 1, and 8. That rules out 2, 6, 7, and 9 from the row’s list.
Only 5 remains. The center box has no 5, so you can place it there.

This is a single-candidate move. One number fits the cell after you apply all three rules.

Keep going without guessing

After placing a number, scan the affected row, column, and box again. Your move may leave another cell with just one possibility. If several numbers still fit, leave the cell empty or write small candidate notes.

Being unable to see a move right away is normal. Work elsewhere on the board and return to it. A completed row is useful progress even if the rest of the puzzle takes longer.

Check your result

When the board is full, check that every row, column, and box contains 1 through 9 once each. The practice page includes a separate solution you can open when you are ready.

Continue with two beginner Sudoku strategies, or choose a readable app to practice on your iPhone.