Classic Sudoku.
Learn the rules, see the possibilities.
A quiet challenge with one clear goal: complete the grid using logic. In a standard 9×9 Sudoku, every row, column, and 3×3 box must contain the numbers 1–9 exactly once. Start with the clues already on the board, then use what is missing to find your next move.
How to play Classic Sudoku
Three ideas. Illustrated on the board. Take them one move at a time.
Read across a row
Start with a row that is nearly complete. List the digits it already contains and compare them with 1–9. If only one digit is missing, that digit belongs in the empty cell. The example highlights the entire first row so you can follow it from left to right.
Here, 1, 2, 3, 4, 6, 7, 8, and 9 leave just one possibility: 5.
Look down the column
The same rule works from top to bottom. A digit cannot repeat anywhere in a column, even when the cells are in different boxes. Before placing a number, check its full column as well as its row. A number that fits one direction may be ruled out by the other.
Scan all nine cells, not just the three cells inside the current box.
Bring the 3×3 box into the picture
Thicker lines divide a 9×9 board into nine 3×3 boxes. Every box also needs a complete set of 1–9. Combine the box rule with the row and column rules: the correct value for a cell must satisfy all three groups at the same time.
Use Notes to record candidates when more than one number still fits.
Sudoku strategies that work in every variant
Every Sudoku is solved with the same three habits. They need no arithmetic and no guessing — just a careful look at what each cell can still be.
Scan rows, columns, and boxes
Pick a number and sweep the grid. Where a number already appears, it cannot go again in that row, column, or box. Three placed copies often leave only one open cell for the fourth.
Hunt for singles
Look for a cell with just one possible symbol left. A row or box that is almost complete is the fastest place to find one, and each single you place narrows the next cell.
Write candidates, then eliminate
When two or three cells stay open, switch on Notes and pencil in the possibilities. Cross out candidates as peers fill in. If a digit fits only one cell inside a group, that cell must hold it.
A few Classic Sudoku facts
Cells in a standard grid
Nine rows multiplied by nine columns.
Groups to check
Nine rows, nine columns, and nine boxes.
Sum of a complete unit
The digits 1 through 9 add up to 45.
These examples and figures describe a standard 9×9 board unless otherwise stated.
Make yourself at home on the board.
Choose a cell, enter a symbol, and keep going. Use Notes for possibilities, Undo to revisit a move, and Hint when you need a nudge. Change the visual theme without changing your game.
- ↑↓←→
- Move between cells
- 1–9
- Enter a number; use the keypad for larger symbol sets
- Del
- Erase your entry
- Ctrl / ⌘Z
- Undo the last move
Classic Sudoku, explained.
A few things you might be wondering.
Do I need mathematics to solve Classic Sudoku?
No arithmetic is required for Classic Sudoku. The digits are symbols, and the puzzle is solved by checking where each symbol can appear without repeating.
What is the best first move for a beginner?
Look for a row, column, or box with only one empty cell. If none exists, choose a nearly complete group and use the intersecting rows and columns to eliminate candidates.
Can I play smaller or larger Sudoku grids?
Yes. Classic Sudoku on Sudokuzz supports 4×4, 6×6, 9×9, 12×12, and 16×16 boards. The symbol set and rectangular box dimensions change with the selected size.