How to play Sudoku

Sudoku is a logic puzzle in which you fill a grid with digits so that every row, column and box holds each digit exactly once.

Fill the grid so every row, column and box holds 1 to 9.

About Sudoku

The classic puzzle starts with some digits already in place. These givens are fixed and cannot be changed; you fill in the rest from them.

The givens are part of the one solution, so they are never the mistake: every conflict marked in a classic puzzle involves at least one digit you entered. The rating tells you which techniques to expect, and a classic Easy board can be finished with singles alone.

Start with the digits that appear most often among the givens. For each box still missing one of them, rule out the rows and columns where it already stands; often a single cell is left. If an Easy board stalls, a single has been missed, so scan again before reaching for notes or a hint.

The goal of Sudoku

Fill every empty cell so that each row, each column and each box holds every digit exactly once. The classic grid is nine by nine, with nine boxes of three by three and the digits 1 to 9; the 6x6 grid has six boxes of two rows by three columns and the digits 1 to 6. Every puzzle has exactly one solution.

How to set up Sudoku

Choose Easy, Medium, Hard or Any as the difficulty of your next new puzzle. Easy puzzles need only the simplest deductions, Medium ones also need eliminations such as pointing pairs and naked pairs, and Hard ones need techniques beyond those.

Sudoku rules

Select a cell and enter a digit. Turn on Notes to pencil in candidate digits instead; notes are reminders, not moves, and writing a digit in a cell clears its notes. Erase empties a cell, Undo takes back your last move, and Restart lays the same puzzle out again.

A digit repeated in a row, column, box or cage is marked as a conflict, and so is a full cage that does not add up to its sum. A digit that breaks no rule but is still wrong is left unmarked, unless you turn on Check entries in the settings.

Hint fills in the next cell that logic forces from your current position, or points out your first wrong entry. Hints are unlimited, but a puzzle finished after a hint, or with Check entries on, is not recorded as a win.

How to win at Sudoku

The puzzle is solved as soon as the grid is full and no rule is broken.

The finished board shows how many moves you made and how long you took. If you are signed in, the win is added to your record, unless you took a hint or had Check entries on.

Sudoku strategy tips

Use notes where the grid is crowded. When two cells in one row, column or box can only hold the same two digits, no other cell of that row, column or box can hold them.

In Killer Sudoku, every row, column and box adds up to 45, and very small or very large cage sums allow few combinations: two cells summing to 3 can only be 1 and 2, and two summing to 17 only 8 and 9.

Look for hidden singles as well as naked ones: when a digit has only one possible cell left in a row, column or box, it goes there, even if that cell could still hold other digits.

When every candidate for a digit inside a box lies in one row or column, that digit cannot appear anywhere else in that row or column outside the box. It works the other way round too, from a row or column into a box.

Sudoku questions and answers

Does every Sudoku puzzle on this site have only one solution?

Yes. Every puzzle, classic or Killer, is checked to have exactly one solution before it is shown. In a classic puzzle a clue is only removed if the grid still has a single answer, and a Killer cage layout is thrown away unless the cages alone fix one answer. You never have to guess between two valid grids.

How many numbers does a classic Sudoku start with?

A classic Sudoku here starts with at least 23 givens. Clues are removed down to a target between 23 and 28, and any clue whose removal would allow a second solution stays, so some puzzles show more. Killer Sudoku starts with no givens at all; its cage sums do that job instead.

How many numbers does a 6x6 Sudoku start with?

A 6x6 Sudoku here starts with at least 8 givens. Clues are removed down to a target between 8 and 13, and any clue whose removal would allow a second solution stays, so some puzzles show more. 6x6 Killer Sudoku starts with no givens at all, like Killer Sudoku.

Are 6x6 Sudoku puzzles easier than 9x9 ones?

Usually. Most 6x6 puzzles can be finished with singles alone and rate Easy. Medium and Hard ones are rare, so when you choose one of those the game looks through fresh puzzles for one that rates as asked. 6x6 Killer Sudoku rates Medium or Hard more often, because its cages hide their digits.

What makes a Sudoku Easy, Medium or Hard?

The techniques it needs, not the number of givens. A solver rates every puzzle: Easy falls to naked and hidden singles, Medium also needs pointing pairs, box-line reduction or naked pairs, and Hard needs something beyond those. The puzzle in play shows its rating, and Any deals whichever puzzle comes next, whatever it rates.

Is there a daily Sudoku puzzle?

Yes. Sudoku, Killer Sudoku, 6x6 Sudoku and 6x6 Killer Sudoku each have a daily board, and everyone gets the same puzzle that day. The daily is dealt as it is, whatever it rates, so your difficulty choice does not apply to it.