What is a hidden single in Sudoku?
A hidden single is a digit that can appear in only one cell of a row, column, or box, even if that cell contains other notes.
Pure Sudoku
Beginner technique
Hidden singles keep a crowded Sudoku moving.
A cell may show several candidates, yet one digit can still be forced when it has no other valid position in the row, column, or box.
- Level
- Beginner
- Pattern
- One digit, one possible position in a unit
- Outcome
- Logical progress
Focused example
Candidate 5 appears in only one cell of this row.
The highlighted cells show the exact scope of the pattern. Read the candidates before making an elimination.
How it works
Apply the pattern in four checks.
- Choose one row, column, or box and pick a missing digit.
- Check every empty cell in that unit for the digit.
- If only one cell can contain it, place the digit there.
- Update the affected candidates and scan the unit again.
Know the difference
Use the pattern only when every condition is true.
A naked single has one candidate inside its cell. A hidden single may have several notes, but its digit has only one possible position in the whole unit.
After the move, re-scan the affected unit for singles before searching for another advanced pattern.
Common mistake
Protect the logic before erasing a candidate.
Do not call a candidate hidden until you have checked every other empty cell in the same row, column, or box.
If any required condition is missing, leave the candidates in place and continue scanning.
Continue playing
Choose your next Sudoku route.
FAQ
Quick answers before you play.
How do I find hidden singles faster?
Scan one missing digit at a time across a full unit instead of reading one cell at a time.
Are hidden singles a beginner technique?
Yes. They are one of the first reliable techniques to learn after the basic Sudoku rules.
Practice loop
Find it on a live board.
Pause when the board slows down, check the candidate conditions, make one justified move, and scan again.