The Three Rules
Sudoku has three rules. Every row has the digits 1 through 9 with no repeats. Every column has the digits 1 through 9 with no repeats. Every 3x3 box has the digits 1 through 9 with no repeats. That is it. No math. No adding. Just placement.
The Grid
A standard Sudoku grid has 81 cells. Nine rows and nine columns. The grid is split into nine 3x3 boxes. Some cells come pre-filled. These are called givens. The more givens a puzzle has, the easier it is. Easy puzzles might have 40 givens. Expert puzzles can have as few as 17.
Step 1: Scan
Start by scanning the grid. Look for rows, columns, or boxes that already have most of their numbers filled in. If a row has eight numbers, the ninth is obvious. Write it in. Move on.
Step 2: Eliminate
Pick an empty cell. Check its row, column, and box. Cross off every number that already appears. If only one number is left, that is the answer. This is called a naked single and it is the most common move in Sudoku.
Step 3: Hidden Singles
Sometimes a cell has multiple candidates, but one of them can only go in that cell within its row, column, or box. That is a hidden single. For example, if the number 5 can only fit in one cell within a 3x3 box, it must go there.
Step 4: Pencil Marks
For harder puzzles, write small candidate numbers in empty cells. This gives you a visual map of what is possible. As you fill in cells, erase candidates from neighboring cells. Pencil marks are the foundation of every advanced technique.
Step 5: Practice
Start with easy puzzles. Solve 20 before moving to medium. Build your scanning speed. Learn to spot naked singles without thinking hard. The more you practice, the faster you get. Our puzzle books start at easy and go all the way to expert.
Common Mistakes
Guessing is the biggest mistake beginners make. Sudoku is pure logic. If you are guessing, you missed something. Go back and look again. The second mistake is forgetting to check all three constraints: row, column, and box. Always check all three.