Fill every row, column, and 3×3 box with 1–9. No repeats.
Sudoku is a free online logic puzzle where you fill a 9×9 grid so that every row, column, and 3×3 box contains the numbers 1 through 9 with no repeats. Over 100 million people worldwide play Sudoku regularly, making it the most popular number puzzle in the world.
Choose from four difficulty levels — Easy, Medium, Hard, or Expert — each with a different number of starting clues. Use logic to fill in the missing numbers. Features include a notes mode for pencil marks, undo, limited hints, error highlighting, and a timer to track your solving speed.
Sudoku is a logic puzzle played on a 9×9 grid divided into nine 3×3 boxes. Fill each row, column, and 3×3 box with the numbers 1-9, with no repeats. Start with the given numbers and use logic to deduce the rest — no math or guessing required.
Yes, research suggests Sudoku can improve concentration, logical thinking, and working memory. A 2019 study found that people who regularly solve puzzles like Sudoku have brain function equivalent to people 10 years younger on short-term memory tests.
Expert-level Sudoku puzzles have fewer given numbers (17-22) and require advanced techniques like X-Wing, Swordfish, and XY-Wing to solve. The minimum number of clues for a unique Sudoku solution is 17.
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Last updated: March 2026 · whatifs.fun — Free interactive games, experiments & simulations