How to Play Sudoku: Rules for Absolute Beginners
Sudoku has a reputation for being a math puzzle, but it is not. You do not need addition, subtraction, or any arithmetic beyond counting cells. Sudoku is a logic puzzle - and the rules fit on a napkin. Most beginners are surprised to find a finished puzzle within 20 minutes of starting.
The Grid and the Three Rules
A Sudoku grid is a 9x9 board divided into nine 3x3 boxes. Some cells start filled with digits - those are your clues. Your job is to fill every empty cell with a digit from 1 to 9, subject to three constraints that apply everywhere on the grid.
- Each of the 9 rows must contain the digits 1-9 exactly once.
- Each of the 9 columns must contain the digits 1-9 exactly once.
- Each of the nine 3x3 boxes must contain the digits 1-9 exactly once.
That is the entire rule set. There is one and only one correct solution to every well-formed Sudoku puzzle, and you solve it by finding which digit is the only legal choice for each empty cell.
Four Solving Strategies (From Easy to Hard)
Sudoku solving scales with how many techniques you know. The four below cover about 90% of the puzzles you will see online. Master them in order.
Strategy 1: Single candidate (easy)
Look at any empty cell. Count which digits from 1-9 are already present in its row, column, and 3x3 box. If only one digit is missing, that digit is the answer. This alone solves most easy puzzles.
Strategy 2: Single position (medium)
After scanning individual cells runs out, scan rows, columns, and boxes for the last placement of a specific digit. If digit 5 appears in 8 of the 9 cells of a row, the missing row position becomes the only legal spot for 5 in that box.
Strategy 3: Naked pairs and triples (medium-hard)
When two cells in the same row, column, or box both have exactly the same two candidate digits, those two digits must go in those two cells. You can eliminate those two digits from every other cell in that row, column, or box. Triples extend the same logic to three cells.
Strategy 4: X-wing and swordfish (hard)
These advanced patterns require scanning rows and columns together for repeating candidate patterns. You will not need them to finish 95% of online puzzles. Skip them until you are solving hard puzzles in under 15 minutes and want a new challenge.
Common Beginner Mistakes
Two other common traps. First, do not chase multiple moves at once - place one digit, then re-scan. Second, do not confuse rows with columns when counting placement. The puzzle is symmetric and easy to mix up.
Difficulty Levels Explained
Most online Sudoku games split puzzles into four difficulty bands:
- Easy: 40-45 clues given, single-candidate solves most of the puzzle. Good first 10.
- Medium: 30-35 clues, single-position techniques required throughout.
- Hard: 25-30 clues, candidates and naked pairs are essential.
- Expert: 22-25 clues, X-wing and swordfish appear multiple times.
Start Playing Now
Sudoku translates perfectly to the browser - no pieces, no setup, just a grid and the time you want to spend. Open Sudoku free, pick the Easy difficulty, and apply single-candidate scanning on your first three empty cells. Within five minutes the logic clicks, and most players are hooked for years.
For another logic puzzle with similar mental exercise, try Minesweeper - the constraints are different but the satisfaction of clearing a hard board is identical.
