Play Sudoku Online Free
Fill the 9×9 grid so each row, column, and 3×3 box contains digits 1–9. Three difficulty levels.
How to Play Sudoku
A 9×9 grid is partially filled with numbers. Your task: fill every empty cell with a number from 1 to 9, following three rules: each row must contain 1–9 exactly once, each column must contain 1–9 exactly once, and each 3×3 sub-grid (box) must contain 1–9 exactly once. No guessing is required — every puzzle on this page can be solved through pure logic and deduction. Choose from Easy, Medium, or Hard difficulty depending on your experience level.
Sudoku Strategy — Essential Techniques
1. Scanning (Beginner)
The most basic technique: pick a number (say, 5) and scan every row, column, and box to see where it can legally be placed. If a 5 already exists in a row and a column, the intersection cell cannot be 5. By cross-hatching (scanning rows against columns), you can often narrow a cell down to a single possible number. This technique alone solves most Easy puzzles.
2. Pencil Marks / Candidates (Intermediate)
For each empty cell, mentally (or physically) note which numbers could legally go there — these are called candidates. If a cell has only one candidate, that must be the answer. If a number appears as a candidate in only one cell of a row, column, or box, that cell must contain that number. This is the foundation of all advanced Sudoku.
3. Naked Pairs (Advanced)
If two cells in the same row, column, or box both have exactly the same two candidates (e.g., both can only be 3 or 7), those two numbers are locked to those two cells. You can eliminate 3 and 7 as candidates from every other cell in that row/column/box. This "naked pair" technique cracks most Hard puzzles.
4. Hidden Singles (Advanced)
If a number appears as a candidate in only one cell within a row, column, or box — even if that cell has other candidates — that cell must be that number. The number is "hidden" among other candidates, but its uniqueness in that group makes it the only possible answer for that cell.
5. Do Not Guess
Resist the temptation to try a number "just to see what happens." Every proper Sudoku has a unique solution reachable through logic. Guessing may occasionally work on Easy puzzles, but on Hard puzzles it leads to contradictions that are extremely difficult to unwind. Build the logical deduction habit early.
Sudoku History — From New York to the World
Modern Sudoku was popularized by the Japanese puzzle company Nikoli in 1984, but its roots trace to Leonhard Euler, the 18th-century Swiss mathematician who studied "Latin squares" — grids where each symbol appears exactly once per row and column. The modern 9×9 format with 3×3 boxes was created by American architect Howard Garns and first published in Dell Pencil Puzzles magazine in 1979 under the name "Number Place." It took a Japanese publisher to rename it Sudoku (meaning "single number") and turn it into a global phenomenon. Today, the World Sudoku Championship attracts competitors from over 30 countries.
Frequently Asked Questions
Can I play Sudoku online for free?
Yes — play Sudoku online free right here with Easy, Medium, and Hard difficulty levels. No download, no signup, play directly in your browser.
What is the difference between Easy, Medium, and Hard?
Easy: 40–45 given numbers, solvable with scanning and cross-hatching alone. Medium: 30–35 given numbers, requires pencil marks and candidate elimination. Hard: 25–28 given numbers, requires advanced techniques like naked pairs, hidden singles, and sometimes X-wing patterns. Start on Easy and move up when you can solve consistently.
Is Sudoku good for your brain?
Yes. Sudoku exercises logical deduction, pattern recognition, and working memory. Studies suggest regular Sudoku play improves short-term memory and concentration, particularly in older adults. While it does not prevent dementia, it contributes to building cognitive reserve — the brain's ability to maintain function despite age-related changes.
Can every Sudoku be solved without guessing?
Yes — every puzzle on this page has a unique solution reachable through pure logic. Well-constructed Sudoku puzzles never require guessing. If you find yourself stuck, you are missing a logical deduction, not a lucky guess.
More Puzzle Games to Try
If you enjoy Sudoku, try 2048 for number merging strategy, Sliding Puzzle for spatial reasoning, or Sequence Memory for pattern recall training. See all puzzle games in Puzzle Games.