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Free sudoku, four strengths
Pick a level and a fresh 9×9 grid is dealt on the spot. Every puzzle is checked to have exactly one solution, so it can always be solved by logic.
Easy Sudoku
Plenty of givens. A gentle warm-up.
Medium Sudoku
Fewer givens, a few spots that need notes.
Hard Sudoku
Thin grid. Pencil marks recommended.
Ultra hard Sudoku
Stripped as far as a unique answer allows.
What is sudoku?
Sudoku is a logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. The goal is to fill every row, every column and every box with the digits 1 to 9, each exactly once. Some digits, called givens, are already placed, and the fewer givens a grid has, the harder it usually is.
The modern puzzle first appeared as “Number Place” in Dell Magazines in 1979 and is credited to the American puzzle maker Howard Garns. The Japanese publisher Nikoli popularised it in the 1980s and gave it the name Sudoku.
How to play
- Fill every row, column and 3×3 box with the digits 1 to 9, each used once.
- Tap a cell, then tap a number. On a computer you can type digits and move with the arrow keys.
- Switch on Notes (or press N) to pencil in candidates. Placing a digit clears it from the notes in the same row, column and box.
- Repeated digits turn red straight away. Check marks any cell that differs from the solution; Hint fills one cell for you.
Frequently asked questions
- How many sudoku levels are there?
- Four: Easy (38 givens), Medium (32), Hard (27) and Ultra hard (about 23, as few as the grid allows while keeping one solution).
- What is the minimum number of clues in a valid sudoku?
- 17. In 2012 a computer search by Gary McGuire, Bastian Tugemann and Gilles Civario showed that no 16-clue sudoku has a unique solution.
- Does sudoku need any maths?
- No. The digits are only symbols. Sudoku is pure logic about where each symbol can go.