How to play Sudoku
Sudoku rule: fill the 9×9 grid so that each row, each column and each 3×3 box contains the digits 1 through 9 exactly once. The starting digits can't be changed; logic tells you the rest.
Step-by-step for beginners
- Understand the grid. A Sudoku is a 9×9 grid divided into nine 3×3 boxes. Some cells already contain digits; these are the givens.
- Learn the one rule. Each row, each column and each 3×3 box must contain every digit from 1 to 9 exactly once.
- Scan for easy placements. Pick a digit, say 5, and look at where it already appears. The rows, columns and boxes it occupies are blocked, which often leaves a box with only one spot for 5.
- Find cells with one candidate. For an empty cell, list the digits not yet in its row, column and box. If only one digit is possible, write it in.
- Use notes on harder puzzles. Write small candidate digits in cells (pencil marks). As you place digits, erase them from the notes of related cells until only one remains.
- Finish the grid. Keep alternating between scanning and candidates until every cell is filled. A correctly built Sudoku always has one solution and never requires guessing.
Words you'll see
| Cell | One square of the grid. There are 81. |
|---|---|
| Box (or block) | One of the nine 3×3 squares, outlined with thicker lines. |
| Given | A digit printed at the start. Givens are shown in bold. |
| Candidate | A digit that could still go in a cell. |
| Notes / pencil marks | Small candidate digits you write in a cell to keep track. |
| Single | A cell with only one candidate, or a digit with only one possible cell in a row, column or box. |
Playing on Puzzdoku
- Tap a cell, then a number on the pad (or type 1–9).
- Turn on Notes to write candidates. Placing a digit clears it from related notes automatically.
- Show mistakes marks wrong digits in red. Switch it off for a purer challenge.
- Hint explains the next logical step and highlights the cell.
Play Sudoku now Next: Sudoku techniques
Frequently asked questions
What is the basic rule of Sudoku?
Every row, every column and every 3×3 box must contain the digits 1 to 9 exactly once. There is no arithmetic involved; the digits are just symbols.
Do you need math to play Sudoku?
No. Sudoku uses numbers as labels only. You could replace them with letters or colors and the puzzle would work the same way.
How many givens does a Sudoku need?
A Sudoku with a single solution needs at least 17 givens; that was proven by computer search in 2012. Easy puzzles usually start with 36 to 40.
Is guessing allowed in Sudoku?
You can guess, but you never need to. Every well-made Sudoku, including every puzzle on Puzzdoku, can be solved by logic alone.
How long does a Sudoku take?
An easy puzzle takes most players 5 to 15 minutes, a hard one 20 to 45 minutes. Speed comes from practicing scanning and the techniques in our tips guide.