Single Candidate in Sudoku: How to Spot It
Learn the Single Candidate Sudoku technique: when one cell has only one possible number left.
Visual example
Single Candidate: one cell, one legal number
The highlighted cell is reduced to a single candidate, so the next move is clear.
Quick answer
Single Candidate
A Single Candidate in Sudoku is a cell with only one possible number remaining. Once every other number is ruled out by the row, column, and box, the remaining candidate must be placed in that cell.
Recognition rules
How to spot it
- Choose a cell.
- Check which numbers are already used in its row, column, and box.
- List the remaining candidates.
- If only one candidate remains, place it.
What is a Single Candidate?
A Single Candidate appears when one empty cell has only one possible number left. Every other number has been ruled out by the row, column, and box.
When to look for it
Look for Single Candidates early and often. They are the foundation of Sudoku solving and usually appear before harder techniques are needed.
Why the placement works
Sudoku allows each number once per row, column, and box. If eight numbers are impossible for a cell, the ninth number is forced.
FAQ
What is a Single Candidate in Sudoku?
A Single Candidate is a cell with only one legal number left.
Is Single Candidate the same as Naked Single?
Yes. Many Sudoku guides call this technique a Naked Single.
When should beginners use Single Candidate?
Use it whenever a cell has only one remaining candidate after checking its row, column, and box.
Does Single Candidate require candidate notes?
Candidate notes help, but beginners can also identify the pattern by checking possible numbers manually.
Practice this technique in Sudoku Coach
Read the pattern, then practice it step by step with guided hints that explain why the move works.
Related Sudoku techniques
Hidden Single in Sudoku: How to Spot It
Learn the Hidden Single Sudoku technique: when a number has only one possible position in a row, column, or box.
Naked Pair in Sudoku: How to Spot It
Learn how Naked Pairs work in Sudoku, when to look for them, and how to remove candidates safely.