Sudoku

About Sudoku

Sudoku is the world's most popular logic puzzle. Fill a 9×9 grid so every row, column and 3×3 box contains the digits 1–9 exactly once. Choose from Easy, Medium, Hard, and Expert difficulty levels. Free online, no download needed.

History of Sudoku

Despite its Japanese name meaning "single number," Sudoku was actually invented by American architect Howard Garns and first published as "Number Place" in Dell Magazines in 1979. Japanese puzzle publisher Nikoli discovered it in 1984, refined the rules, and gave it the name Sudoku. The puzzle remained relatively obscure until 2004, when retired Hong Kong judge Wayne Gould convinced The Times of London to publish daily Sudoku puzzles. Within months, the puzzle swept across newspapers worldwide, becoming the most popular logic puzzle in history.

Sudoku Tips & Strategies

• 💡Start with rows, columns, or boxes that already have the most numbers filled in to find easy placements.
• 💡Use pencil marks (candidates) to note possible numbers for each empty cell, then eliminate systematically.
• 💡Look for "naked singles" where only one number can possibly fit in a cell based on row, column, and box constraints.
• 💡Apply the "hidden single" technique: if a number can only go in one place within a row, column, or box, place it there.
• 💡For harder puzzles, learn the "pointing pairs" and "box-line reduction" techniques to eliminate candidates.

Fun Facts About Sudoku

• ★There are exactly 6,670,903,752,021,072,936,960 valid completed Sudoku grids, but only 5,472,730,538 essentially different ones when accounting for symmetry.
• ★The minimum number of given clues required for a Sudoku puzzle to have a unique solution is 17, proven mathematically in 2012.
• ★The world record for solving a standard 9x9 Sudoku puzzle is under 2 minutes, set at competitive speed-solving championships.
• ★Sudoku puzzles are used in cognitive science research as a tool for studying human logical reasoning and pattern recognition.

How to Play Sudoku

1. 1Click an empty cell to select it
2. 2Enter a number from 1-9
3. 3Each row, column, and 3×3 box must contain each number exactly once
4. 4Use pencil marks to note possible numbers for difficult cells

Frequently Asked Questions about Sudoku