How to Play Sudoku — Beginner to Intermediate Guide

Complete rules, examples, step-by-step walkthroughs, and practical solving techniques. Includes an illustrated solved puzzle and tips you can use right away.

What is Sudoku?

Sudoku is a logic-based number placement puzzle. The standard puzzle uses a 9×9 grid divided into nine 3×3 boxes. The objective is to fill every empty cell with a digit from 1 to 9 so that each row, each column, and each 3×3 box contains every digit exactly once.

Basic Rules (Quick)

Rows

Each horizontal row must contain the digits 1–9 without repetition.

Columns

Each vertical column must contain the digits 1–9 without repetition.

3×3 Boxes

Each 3×3 subgrid must have numbers 1–9 exactly once.

No Arithmetic

Sudoku requires logic and deduction, not arithmetic—so anyone can play regardless of math skill.

Beginner Techniques — How to Start Solving

  1. Scan rows and columns: Look for numbers that are already placed and eliminate them as candidates from intersecting cells.
  2. Use pencil marks: Small candidate lists (1–9) inside a cell help track what might fit.
  3. Single candidate (Naked Single): If a cell only has one possible number after elimination, place it.
  4. Single position in a unit (Hidden Single): If within a row/column/box a particular digit can only go into one cell, it must go there.

These basic steps will solve many easy puzzles. When you progress, use the intermediate techniques below.

Step-by-Step Example (Solved Walkthrough)

Below is a solvable example. We'll walk through several steps, showing pencil marks and reasoning. Replace placeholder images with your in-game screenshots for best clarity.

Starting Puzzle

5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
7
9

(This is a common tutorial puzzle—many solvers will recognize it.)

Step 1 — Scan for easy placements

Look for cells that clearly can only be one number. For example, consider the top-left 3×3 box (rows 1–3, cols 1–3). If numbers 5,6,9,8 are already present in oriented rows/columns, sometimes a cell will only accept one candidate.

Step 2 — Use pencil marks to narrow candidates

For a central blank, list possible numbers left (e.g., 2,4). If later one gets eliminated, place the final number.

Step 3 — Hidden singles

If within a row a certain digit can only go in one cell (even if that cell has multiple pencil marks), that's a hidden single — place it.

Step 4 — Continue until completion

Follow these simple deductions repeatedly. When no more singles exist, move to intermediate tactics below.

Intermediate Techniques (When Beginner Logic Stalls)

Naked Pairs / Triples

If two cells in a unit (row/column/box) contain the exact same two candidates (e.g., {2,7} and {2,7}), then those two digits must occupy those cells. You can remove those candidates from other cells in that unit.

Locked Candidates (Pointing / Claiming)

If within a box candidate X can only appear in cells that lie in the same row (or column), then X cannot appear in that row (or column) outside the box — remove it from those cells.

X-Wing

X-Wing uses patterns across two rows and two columns to eliminate candidates. If a candidate appears in only two positions in two different rows and those positions line up in the same two columns, then that candidate can be removed from other cells in those columns.

Swordfish and Advanced Patterns

Swordfish generalizes X-Wing across three rows/columns. These patterns are rarer but powerful for very difficult puzzles.

Practical Tips & Common Mistakes

  • Use pencil marks consistently — they save time and prevent guessing.
  • Don't guess — guessing often leads to contradictions and wasted effort.
  • Work systematically — choose one row/box and fully resolve it before moving on.
  • Keep notes of your reasoning if a puzzle is hard — it helps to backtrack when needed.

FAQ

Q: Are all Sudoku puzzles solvable without guessing?

Most published Sudoku puzzles (especially from reputable sources) are designed to be solvable by logic alone. Extremely difficult puzzles may require advanced techniques, but you should still avoid blind guessing.

Q: How long does it take to get good?

Practice for a few weeks and you'll see big improvements. Start with easy puzzles, then move to medium, using the techniques above.

Play Sudoku Now Advanced Strategies