Number logic
How to Solve Sudoku with Logic
A clear introduction to Sudoku rules, scanning rows and boxes, and finding forced placements without guessing.
The rule behind every move
A standard Sudoku has nine rows, nine columns, and nine 3×3 boxes. Each of those units must contain the numbers 1 through 9 once, so an empty cell is solved by eliminating every number that is already present around it.
The same logic works whether you write notes on paper or use an interactive board. The aim is to find a move that the rules force, not to guess a number that merely looks plausible.
Scan a single number across the board
Pick one number and inspect every 3×3 box. If a row and column leave only one possible square in that box, that number has a forced home.
Then reverse the process: inspect a row or column and ask which number can appear in only one of its remaining empty cells. This simple scan catches many reliable moves.
Keep the puzzle readable
After placing a number, revisit the row, column, and box that changed. One solved cell often creates another forced placement nearby.
If a section becomes confusing, move to a different box rather than guessing. A single confirmed number elsewhere can make the earlier section much clearer.