Sudoku Rules and Strategies

Sudoku is a logic puzzle with simple rules. Whether you are solving your first grid or refining your technique, these rules and strategies will help you progress.

Core Sudoku strategies

Every Sudoku can be solved by pure logic. Here are the basic strategies Sudoked.com uses in its hints.

Last free cell

When only one empty cell is left in a row, column or box, it must contain the only missing digit.

Last remaining cell

When only one cell in a row, column or box can accept a particular digit, that digit must go there.

Last possible number

Look at the digits already present in a cell's row, column and box to find the only digit that can still fit.

Notes in Sudoku

Use pencil marks to list candidate digits in a cell. Good notes make hidden singles, pairs and triples visible.

Naked singles

If a cell's notes leave only one possible digit, that digit is the answer.

Naked pairs

Two cells in the same row, column or box share the same two candidates. Those two digits can be eliminated from the other cells in that house.