Naked Singles & Hidden Singles
The fundamental bedrock of all Sudoku solving. When 8 other numbers occupy a cell's row, column, and box, the cell has only 1 remaining possibility.
Interactive Naked Single Trainer (Center Cell R5C5)
Notice Row 5 contains [1, 2, 3, 4, 6, 7, 8, 9] across its peers. R5C5 has only 1 legal candidate remaining: 5. Click Solve to place it!
Naked Single vs. Hidden Single
| Feature | Naked Single | Hidden Single |
|---|---|---|
| How it's spotted | By examining 1 specific cell and eliminating all seen digits. | By examining 1 specific digit and finding only 1 cell for it. |
| Pencil marks | Only 1 pencil mark candidate is in the cell. | Multiple pencil marks may exist, but the digit appears once in the unit. |
| Difficulty tier | Easy / Medium | Easy / Medium |
Frequently Asked Questions
What is a Naked Single in Sudoku?
A Naked Single (or Sole Candidate) is a cell that has only one possible candidate number remaining after accounting for all numbers already placed in its row, column, and 3×3 box. It is the most basic forced move in Sudoku.
What is a Hidden Single in Sudoku?
A Hidden Single occurs when a digit can only go into ONE cell within a row, column, or 3×3 box, even if that cell contains other candidate numbers as possibilities. Because that house must contain that digit, the cell is forced to take that number.
How do I spot Naked Singles quickly?
Look for cells at intersections of heavily filled rows, columns, and boxes. Count the digits from 1 to 9 present in that cell's row, column, and 3×3 box. If 8 unique digits are visible, the remaining digit is your Naked Single.
Start with Easy Sudoku
Practice spotting singles on our beginner-friendly puzzles with instant hints and check mode.