Naked Single in Sudoku
A Naked Single is one of the simplest and most important Sudoku solving techniques. It happens when an empty cell has only one possible number left. If only one candidate can fit, that number must go in the cell.
Summary
A Naked Single appears when a Sudoku cell has only one possible candidate after checking its row, column, and 3x3 box.
Diagram
- Target
- Blocked
- Focus unit
Table of Contents
What this technique is
A Naked Single is a cell with only one valid number left. The answer is visible directly from the candidates inside that cell.
When to use it
Use Naked Singles throughout the whole puzzle, especially after placing new numbers and updating notes.
How it works
Check the row, column, and 3x3 box connected to an empty cell. Eliminate every number that already appears. If only one number remains, that cell is a Naked Single.
Step-by-step
- Pick an empty cell.
- Check which numbers already appear in the same row.
- Check which numbers already appear in the same column.
- Check which numbers already appear in the same 3x3 box.
- Remove those numbers from the list of possible candidates.
- If only one candidate remains, place it in the cell.
Example
Imagine a cell can only contain 2, 5, or 8 at first. If 2 appears in the same row and 5 appears in the same box, then only 8 remains. That cell is a Naked Single, so the answer is 8.
What Is a Naked Single?
A Naked Single is a Sudoku cell where only one number is possible. It is called 'naked' because the answer is directly visible from the cell's own candidates. You do not need to compare several cells or find an advanced pattern.
Why Naked Singles Are Important
Naked Singles are the foundation of Sudoku solving. Many easy puzzles can be solved mostly with Naked Singles and basic scanning. In harder puzzles, advanced techniques often remove candidates and create new Naked Singles later.
How to Find a Naked Single
Look at an empty cell and list all numbers from 1 to 9 that could fit. Then remove any number already present in the same row, column, or 3x3 box. If only one candidate is left, you have found a Naked Single.
Naked Single vs Hidden Single
A Naked Single is about one cell having only one candidate. A Hidden Single is different: the cell may have several candidates, but one number can go in only one place within a row, column, or box.
Beginner Tip
After every new number you place, scan nearby cells again. A single placement can remove candidates from several cells and reveal new Naked Singles.
When Naked Singles Stop Appearing
If there are no Naked Singles left, do not guess. Switch to Hidden Singles, Naked Pairs, or other candidate-based techniques. Hard Sudoku puzzles often require several rounds of candidate elimination before another Naked Single appears.
Common Mistakes
- Forgetting to check the 3x3 box.
- Checking only the row and column.
- Placing a number before confirming it is the only candidate.
- Not updating notes after placing a number.
- Confusing Naked Singles with Hidden Singles.
FAQ
Everything you need to enjoy Sudoku with calm, focused play.
What is a Naked Single in Sudoku?+
A Naked Single is an empty cell that has only one possible number left after checking its row, column, and 3x3 box.
Is Naked Single a beginner Sudoku technique?+
Yes. Naked Single is one of the first techniques every Sudoku beginner should learn.
How do you find Naked Singles?+
Check the possible candidates for an empty cell. If only one number can fit, that number is a Naked Single.
What is the difference between Naked Single and Hidden Single?+
A Naked Single has only one candidate in the cell. A Hidden Single is the only place for a number inside a row, column, or box, even if the cell has several candidates.