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.
Visual example
Hidden Single: only one place for the number
Scan the row: candidate 5 appears only in the blue cell, even though that cell has other candidates.
Quick answer
Hidden Single
A Hidden Single in Sudoku is when a number can go in only one cell within a row, column, or box. The cell may have several candidates, but that number has only one possible position in the unit, so it must be placed there.
Recognition rules
How to spot it
- Choose one row, column, or box.
- Pick a number that is not solved in that unit.
- Check every empty cell where that number could go.
- If there is only one possible cell, place the number there.
What is a Hidden Single?
A Hidden Single happens when a number has only one possible position inside a row, column, or box. The cell may still show multiple candidates, but that number is forced.
When to look for it
Look for Hidden Singles after scanning for obvious Single Candidates. Pick a unit and ask where each missing number can still go.
Why the placement works
If a row still needs a 5 and only one empty cell in that row can accept 5, then 5 must go there. Other candidates in that cell do not matter.
FAQ
What is a Hidden Single in Sudoku?
A Hidden Single is a number that has only one possible position in a row, column, or box.
How is Hidden Single different from Single Candidate?
Single Candidate focuses on one cell with one candidate. Hidden Single focuses on one number with one possible position in a unit.
Why is it called hidden?
It is hidden because the target cell may still have multiple candidates, even though one number is forced there.
Is Hidden Single beginner-friendly?
Yes. It is one of the most important beginner techniques after Single Candidate.
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
Single Candidate in Sudoku: How to Spot It
Learn the Single Candidate Sudoku technique: when one cell has only one possible number left.
Hidden Pair in Sudoku: How to Spot It
Learn how Hidden Pairs work in Sudoku, why they are harder to see than Naked Pairs, and how to clean up candidates.