How to play sudoku

Three rules, a few techniques, and you can solve any puzzle on this site.

The rules

A sudoku is a 9×9 grid split into nine bold 3×3 boxes. Some cells start filled in. Fill the rest so that:

• every row contains the numbers 1 to 9 exactly once,
• every column contains the numbers 1 to 9 exactly once, and
• every 3×3 box contains the numbers 1 to 9 exactly once.

That's all. There is no math involved: the numbers are just nine different symbols. Every puzzle on Sudoku Ultimate+ has exactly one solution, so you never have to guess.

Technique 1: scanning

Pick a number, say 5, and look at one box. Every row and column that already has a 5 rules out the cells it crosses in that box. If only one cell is left, the 5 goes there. Scanning each number across all nine boxes solves most Easy puzzles on its own.

Technique 2: the last empty cell

When a row, column or box has eight numbers, the missing one fills the last cell. Look for nearly finished lines after every move. One placement often unlocks the next.

Technique 3: pencil marks

Turn on Notes (or press N) and write the small candidate numbers each cell could still hold. A cell with only one candidate is solved (a "naked single"). A number that appears as a candidate in only one cell of a row, column or box belongs there (a "hidden single"). When you place a number, Sudoku Ultimate+ clears that candidate from the cells it affects.

Technique 4: pairs

If two cells in the same row hold exactly the same two candidates, for example 3 and 7, those two numbers must go in those two cells. You can erase 3 and 7 from every other cell in that row. The same works in a column or box. This "naked pair" is the key step in many Medium and Hard puzzles.

Technique 5: pointing

If, inside one box, all the possible spots for a number sit in the same row, that number has to be in that row within the box. So you can remove it from the rest of that row outside the box. This "pointing pair" clears the way in Hard and Expert puzzles.

Which difficulty should I pick?

• Easy: scanning and last-cell moves are enough. Great for learning and quick breaks.
• Medium: you'll want pencil marks.
• Hard: expect pairs and pointing.
• Expert: fewer starting numbers and longer chains of logic. Patience wins.

Controls on Sudoku Ultimate+

• Keyboard: 1–9 to enter, arrow keys to move, N for notes, Space to pause, Ctrl+Z undo, Ctrl+Y redo.
• Phone: tap a cell, then a number on the pad below the board.
• Hints: your first hint each game is free. More hints cost points (single-player only).
• Mistakes are counted, but you can keep going.

Ready?

Play a free puzzle now, try today's daily puzzle, or race a friend on the same board.