Pick a digit, say 1. Look at each box and ask: where can the 1 go? Scan the rows and columns that already contain a 1 — those lines are blocked.
How to Play Sudoku
The complete beginner's guide — the rules, the grid, and your first solve, step by step.
The goal in one sentence
Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9, each exactly once. That is the entire game — and it never requires arithmetic, only logic.
The three rules
- Rows: each of the nine horizontal rows must contain 1–9 with no repeats.
- Columns: each of the nine vertical columns must contain 1–9 with no repeats.
- Boxes: each of the nine 3×3 boxes must contain 1–9 with no repeats.
A correct Sudoku has exactly one solution. The numbers printed at the start are the givens (or clues); your job is to deduce the rest.
Grid anatomy
- Cell — a single square that holds one digit.
- Row — nine cells across.
- Column — nine cells down.
- Box — a 3×3 block of nine cells.
- Given — a clue printed at the start; it never changes.
- Candidate — a digit that could still go in an empty cell.
Your first solve, step by step
If a box has only one empty cell where 1 is still allowed, place it. This is scanning, also called cross-hatching.
Move through 2, 3, 4 … repeating the sweep. Early on, several placements appear this way.
When scanning stalls, look for naked singles: an empty cell where eight of the nine digits already appear in its row, column or box, leaving exactly one option.
Keep alternating between scanning and singles. Each number you place unlocks new ones until the grid is full.
Common beginner mistakes
- Guessing. If you cannot prove a placement, you have not found it yet — keep looking.
- Ignoring pencil marks. On medium and up, notes are how you see hidden patterns.
- Forgetting the box. Beginners watch rows and columns but overlook the 3×3 box constraint.
- Filling the easy cells and stopping. Re-scan after every placement; the grid changes constantly.
Ready to try it live? Open an easy puzzle and solve along — the board flags mistakes instantly, so you learn as you go.
Frequently asked questions
Is there any math in Sudoku?
No. The digits are just symbols; you could use nine colours instead. Sudoku is pure logic, not arithmetic.
How long should a Sudoku take?
An easy puzzle takes a few minutes; expert and evil grids can take far longer. Speed comes with practice.
What is the best first step?
Scanning for a single digit across all nine boxes. It produces the quickest early placements.