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Naked Singles

Beginner

A cell where only one number can possibly go.

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Example diagram — highlighted cells show where the technique applies.

How It Works

Naked Singles is the most basic Sudoku technique. When a cell has only one possible candidate remaining after eliminating all numbers that appear in its row, column, and box, that number must go in that cell.

Step by Step

  1. Pick an empty cell.
  2. Check which numbers 1-9 already appear in the same row.
  3. Eliminate those from the column as well.
  4. Eliminate those from the 3x3 box.
  5. If only one number remains, that is the answer.

When to Use

Use Naked Singles whenever you have empty cells and want to find quick placements. This is the first technique to try on every puzzle — it works from the easiest to the hardest grids.

Example

Imagine a row has 1, 2, 3, 4, 5, 6, 7, and 8. The only empty cell in that row can only be 9. Similarly, check the column and box; if only one number is missing from all three, that cell is a naked single.

Common Mistakes

Forgetting to check all three constraints (row, column, box) before placing a number. Rushing and placing a number that conflicts with a cell you haven't looked at yet.

Tips

Always start by scanning rows, columns, and boxes that are almost complete. Use pencil marks to track candidates — when a cell has only one candidate left, you've found a naked single.

Practice This Technique

Try solving a puzzle and look for opportunities to apply Naked Singles.

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