How to Play Sudoku: The Complete Beginner's Guide

Sudoku looks intimidating the first time you see it: nine rows, nine columns, nine boxes, and a stack of empty cells waiting to be filled in. The rules themselves are smaller than the grid suggests. Once you have them, the rest is pattern recognition that builds with practice.

The three rules

A standard Sudoku puzzle is a 9×9 grid divided into nine 3×3 boxes. The puzzle starts with some cells already filled in — these are the givens. Your job is to fill every empty cell with a digit from 1 to 9 such that:

1. Each row contains every digit from 1 to 9 exactly once.
2. Each column contains every digit from 1 to 9 exactly once.
3. Each 3×3 box contains every digit from 1 to 9 exactly once.

That is the entire rule set. Every solving technique you will ever learn — from naked singles to forcing chains — is just a way of applying these three constraints to different parts of the grid.

Your first move: the naked single

Pick any empty cell. Look at its row, its column, and its 3×3 box. Cross off every digit that already appears in any of those three groups. If exactly one digit survives, that digit goes in the cell.

This is called a naked single, and on easy puzzles it will solve most of the grid by itself. Beginner puzzles are graded by how often naked singles are available — easy puzzles let you find them everywhere, harder puzzles force you to use other techniques first.

Your second move: the hidden single

Now look at a row, column, or box as a whole. Pick a digit that hasn't been placed in that group yet. Ask: of the empty cells in this group, how many could legally hold this digit? If the answer is exactly one, that's where the digit goes — even if other digits could also fit there.

This is the hidden single, and it's the move that unlocks medium puzzles. The trick is the perspective shift: instead of asking "what digit goes in this cell?", you ask "where in this group does this digit go?".

Pencil marks: how to track candidates

When you can't immediately solve a cell, make a note of every digit that could legally go there. These small notes are called pencil marks or candidates. As you solve cells elsewhere, those candidate lists shrink — and a cell that drops to one candidate becomes a naked single.

Most digital Sudoku tools, including ours, give you a way to enter pencil marks. On paper, write the candidates small in the corners of the cell.

Habits that separate beginners from improvers

A few habits will move you forward faster than any specific technique:

• Always start with the digit that appears most often in the givens. That digit has the fewest possible homes in the empty cells, and you'll often place it everywhere quickly.
• Don't guess. Every move should be justifiable from the rules. Guessing turns a logic puzzle into trial-and-error, and once you've made a wrong guess deep in the grid, unwinding it is harder than just restarting.
• Pencil mark deliberately. Beginners often skip pencil marks and end up stuck. Filling in candidates for ten or twenty empty cells will reveal moves you couldn't see otherwise.
• If you're stuck, scan a different group. When a row offers nothing, try the columns. When columns are quiet, try the boxes.

What's next

Once naked and hidden singles stop solving the puzzle on their own, you'll need pairs and pointing pairs — moves that work on two cells at a time rather than one. We cover those in the techniques section, with interactive examples you can step through.

For now: pick an easy puzzle, give yourself thirty minutes, and treat your first solve as practice rather than a test. Sudoku rewards patience, and patience is the easiest of all the techniques to learn.