How to Solve Sudoku for Beginners

The three rules (and that's all there is)

A Sudoku puzzle is a 9×9 grid divided into nine 3×3 boxes. Some cells are filled in for you; your job is to fill the rest. Three rules govern the whole game:

1. Every row must contain the digits 1 through 9, each exactly once.
2. Every column must contain the digits 1 through 9, each exactly once.
3. Every 3×3 box must contain the digits 1 through 9, each exactly once.

That's it. Every solving technique you will ever learn is just a clever way of applying those three rules together.

What you need before you start

On paper, a pencil and an eraser. Online, a puzzle board with a pencil marks mode (sometimes called "candidates" or "notes"). Pencil marks are small numbers you write inside an empty cell to track which digits could still go there. They are the single most important habit in Sudoku — beginners who skip pencil marks plateau at Easy difficulty and never get further.

Most digital boards, including SudokuHint, let you toggle a pencil-mark mode with one click or one key press.

Technique 1: Naked Singles

A Naked Single is a cell where 8 of the 9 digits are already used in its row, column, or box — leaving only one possibility. That last digit is forced.

To find Naked Singles, scan the empty cells one by one. For each cell, mentally walk its row, its column, and its 3×3 box, and cross off any digit you already see. If only one digit survives, that cell is solved.

In any Easy puzzle, Naked Singles are usually enough to solve the entire board. Just scan, fill in, and re-scan — every digit you place can create new Naked Singles elsewhere. The full walkthrough lives on the Naked Singles technique page.

Technique 2: Hidden Singles

Sooner or later, no cell has only one candidate. Naked Singles run out. That is when Hidden Singles take over.

A Hidden Single flips the question. Instead of asking "what digits can fit in this cell?", ask "where in this row, column, or box can this digit go?" If only one cell has room for that digit, the digit must land there — even if that cell still shows multiple candidates.

Hidden Singles are the technique that unlocks Medium puzzles. They feel slightly less obvious than Naked Singles, but the muscle memory comes fast — usually after solving three or four Medium-difficulty boards. Detailed examples are on the Hidden Singles technique page.

The solving order that actually works

Beginners often jump between cells at random and get overwhelmed. A reliable order:

1. Scan for obvious Naked Singles first. Cells with only one or two other digits visible in their row, column, and box are quick wins.
2. Fill in pencil marks for every empty cell. This is the moment most beginners skip — don't. Spending three minutes on pencil marks now saves twenty minutes of guessing later.
3. Scan for Hidden Singles digit by digit. Pick the digit 1. Walk every row, every column, every box. For each unit, count how many cells could hold a 1. If exactly one, place it. Then move on to digit 2. And so on.
4. After every placement, re-scan for Naked Singles. A single new digit on the board often cascades into three or four more.
5. If you get stuck, that means a more advanced technique applies. See the section below.

A worked example: solving a Medium puzzle in 4 moves

Imagine you are mid-puzzle. Row 5 already contains 2, 4, 5, 7, 8, 9 — six digits in. Three cells in row 5 remain empty, and the missing digits are 1, 3, and 6.

Look at the first empty cell, R5C2. Its column already contains 1 and 6. So R5C2 must be 3 — a Naked Single. Place it.

Now look at the digit 6 across row 5. Two cells remain (R5C7 and R5C9). Cell R5C7 sits in a 3×3 box that already contains a 6. So the only cell in row 5 that can hold 6 is R5C9 — a Hidden Single. Place it.

By elimination, R5C7 must be 1. Row 5 is fully solved.

That solved row 5 means new digits ripple outward into adjacent rows, columns, and boxes. Re-scan, and a new Naked Single will almost certainly appear within five seconds. This is the rhythm of solving Medium puzzles: place a digit, re-scan, place another, re-scan.

What to do when you get stuck

On Hard and Expert puzzles, Naked Singles and Hidden Singles alone are not enough. You will hit a point where no cell is forced. That is your cue to learn the intermediate techniques:

• Naked Pairs — two cells in the same unit sharing the same two candidates lock those two digits away from every other cell in the unit.
• Hidden Pairs — the same idea, but the pair is buried under extra candidate noise.
• Pointing Pairs — when a digit in a box is restricted to one row or column, it clears the digit from the rest of that line.
• Box-Line Reduction — the mirror: when a digit in a row or column is restricted to one box, it clears the digit from the rest of that box.

These four techniques, in order, will get you through every Hard puzzle. Expert puzzles bring in X-Wings, Y-Wings, and a handful of chain-based techniques — but those are for another day.

Common beginner mistakes

• Skipping pencil marks. The single most common reason beginners stall. Without candidates, you cannot see Hidden Singles, Naked Pairs, or anything past Easy.
• Guessing. A well-formed Sudoku puzzle has exactly one solution and can always be solved by logic. If you guess and the puzzle fails three steps later, you have to undo every move since the guess. Logic is faster.
• Filling in the same digit you just used. When you place a 7, scan everywhere a 7 could now be ruled out before placing anything else. The cascade is where the joy lives.
• Starting with Hard difficulty. Naked Singles and Hidden Singles need ~10 Easy and ~5 Medium puzzles to become automatic. Then Hard becomes fun instead of frustrating.
• Erasing pencil marks too eagerly. When you place a digit, only clear candidates that are directly ruled out (same row, column, or box). Do not clean up unrelated cells.

Where to practice

Reading about Sudoku is fine. Playing it is what builds the skill. Open a free puzzle on SudokuHint and start on Easy. When you get stuck, tap the 💡 Hint button — instead of giving the answer, it explains which technique applies and where to look. That is the fastest path from beginner to fluent.

One Easy puzzle a day, for two weeks. Then one Medium puzzle a day, for two weeks. After a month you will read a Sudoku board the way a chess player reads a position — instantly seeing where to look first.

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Article draft v1 · pending native-speaker review