Sudoku Solving Techniques: From Beginner to Expert (2026 Guide)

Sudoku Rules in 30 Seconds

Sudoku is played on a 9×9 grid divided into nine 3×3 boxes. Your goal: fill every empty cell with a number from 1 to 9 such that each row, each column, and each 3×3 box contains each of the digits 1–9 exactly once. No number can repeat within any row, column, or box. That's it. The puzzle is always logically solvable — you never need to guess.

Technique 1: Naked Single Easy

A Naked Single is the most basic technique: a cell where only one digit is possible after eliminating all the numbers already present in its row, column, and box. Start every puzzle by scanning for naked singles — they're your free placements. In Easy puzzles, naked singles alone will solve most of the board.

How to find them: Look at each empty cell and list the numbers 1–9. Cross off any number that already appears in the same row, column, or box. If only one number is left — that's your answer. Fill it in immediately.

Technique 2: Hidden Single Easy

A Hidden Single occurs when a digit can only go in one cell within a particular row, column, or box — even if that cell appears to have multiple candidates. The number is "hidden" among other possibilities.

How to find them: Pick a digit (say, 7) and look at a specific row. Find all the empty cells in that row where 7 could possibly go. If only one empty cell can contain 7 (because 7 already exists in the intersecting columns or boxes of all other empty cells) — that cell must be 7. Repeat this for every digit in every row, column, and box.

Technique 3: Pointing Pairs Medium

A Pointing Pair (or triple) occurs when a digit within a 3×3 box can only appear in cells that all share the same row or column. Because that digit must go somewhere in that box, it must go in that row or column — which means you can eliminate that digit from all other cells in that row or column outside the box.

Example: In the top-left box, the digit 4 can only appear in row 2. Even though you don't know which cell in row 2 within the box holds the 4, you know for certain that 4 cannot appear anywhere else in row 2 (outside that box). Eliminate 4 from all other row-2 cells in the other boxes.

Technique 4: Box-Line Reduction Medium

Box-Line Reduction is the reverse of Pointing Pairs. If a digit in a row or column can only appear within a single 3×3 box, you can eliminate that digit from all other cells in that box.

Example: In row 5, the digit 6 can only appear in cells that are all inside the middle-right box. Therefore, 6 cannot appear anywhere else in that box (outside of row 5). Eliminate 6 from all non-row-5 cells in the middle-right box.

Technique 5: Naked Pairs Hard

A Naked Pair exists when two cells in the same row, column, or box share exactly the same two candidates — and no other candidates. Because those two digits must occupy those two cells (in some order), they can be eliminated from all other cells in the same row, column, or box.

Example: In a column, two cells both have only the candidates {3, 7}. You don't know which cell gets 3 and which gets 7, but you know for certain that 3 and 7 live in those two cells. Remove 3 and 7 from the candidate lists of every other cell in that column.

Technique 6: X-Wing Expert

The X-Wing is one of the first advanced techniques and it's surprisingly elegant. Look for a digit that appears as a candidate in exactly two cells in each of two different rows — and both rows have those candidates in the same two columns. These four cells form a rectangle (the "X"). Because the digit must appear in one of the two cells in each row, it must also appear in exactly one cell in each of those two columns. Therefore, you can eliminate that digit from all other cells in those two columns.

X-Wings are rare but enormously powerful when they appear on Hard and Expert puzzles. Training yourself to spot rectangular candidate patterns is the key habit for expert-level Sudoku play.

Using Pencil Marks Effectively

Pencil marks (also called candidate notation) are small numbers written in the corners of empty cells listing all possible values for that cell. They transform Sudoku from a memory exercise into a visual analysis problem. Here's how to use them efficiently:

• Fill in naked singles first before writing any pencil marks — it reduces the total cells you need to annotate.
• Update pencil marks immediately whenever you place a number — remove that number from all cells sharing the same row, column, and box.
• Scan for hidden singles in your pencil marks before reaching for advanced techniques — they're often hiding in plain sight.
• Highlight specific digits when hunting for X-Wings or Pointing Pairs — focus on one digit at a time rather than looking at all candidates simultaneously.

Our Sudoku game supports pencil marks — tap the pencil icon and then tap cells to add candidate numbers. Use it on Medium and Hard puzzles where naked singles alone won't carry you to the solution.

Frequently Asked Questions