Naked Single

Level 2 · White Belt (Yellow Stripe)

Strategy:

Requires:

Learn after:

Overview

A Naked Single is the simplest pencilmark technique. When a cell has only one candidate remaining (after all eliminations from its row, column, and block), that candidate must be the solution.

How It Works

Enable pencilmarks to see all candidates for each cell.
Look for any cell that has only one candidate remaining.
That candidate is the solution for the cell.

Example

Look for Naked Single.

Sudoku grid showing the initial puzzle state for Look for Naked Single.

1

Naked Single

Check cell r2c2 and examine its candidates.

Sudoku grid illustrating step 1: Naked Single — Check cell r2c2 and examine its candidates.

2

Naked Single

Digit 1 cannot go in r2c2 because r1c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 2: Naked Single — Digit 1 cannot go in r2c2 because r1c2 is already in this column. Remove the entry or choose a different digit.

3

Naked Single

Digit 2 cannot go in r2c2 because r2c9 is in this row, r9c2 is in this column, and r1c3 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 3: Naked Single — Digit 2 cannot go in r2c2 because r2c9 is in this row, r9c2 is in this column, and r1c3 is in this box. Remove the entry or choose a different digit.

4

Naked Single

Digit 3 cannot go in r2c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 4: Naked Single — Digit 3 cannot go in r2c2 because r3c2 is already in this column. Remove the entry or choose a different digit.

5

Naked Single

Digit 4 cannot go in r2c2 because r2c5 is in this row, r7c2 is in this column, and r3c1 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 5: Naked Single — Digit 4 cannot go in r2c2 because r2c5 is in this row, r7c2 is in this column, and r3c1 is in this box. Remove the entry or choose a different digit.

6

Naked Single

Digit 5 cannot go in r2c2 because r4c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 6: Naked Single — Digit 5 cannot go in r2c2 because r4c2 is already in this column. Remove the entry or choose a different digit.

7

Naked Single

Digit 7 cannot go in r2c2 because r2c4 is in this row, r6c2 is in this column, and r1c1 is in this box. Remove the entry or choose a different digit.

Sudoku grid illustrating step 7: Naked Single — Digit 7 cannot go in r2c2 because r2c4 is in this row, r6c2 is in this column, and r1c1 is in this box. Remove the entry or choose a different digit.

8

Naked Single

Digit 8 cannot go in r2c2 because r5c2 is already in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 8: Naked Single — Digit 8 cannot go in r2c2 because r5c2 is already in this column. Remove the entry or choose a different digit.

9

Naked Single

Digit 9 cannot go in r2c2 because r2c1 is in this row and r8c2 is in this column. Remove the entry or choose a different digit.

Sudoku grid illustrating step 9: Naked Single — Digit 9 cannot go in r2c2 because r2c1 is in this row and r8c2 is in this column. Remove the entry or choose a different digit.

10

Naked Single

This cell has only one candidate remaining: 6.

Sudoku grid illustrating step 10: Naked Single — This cell has only one candidate remaining: 6.

11

Naked Single

This is a Naked Single - the cell is forced.

Sudoku grid illustrating step 11: Naked Single — This is a Naked Single - the cell is forced.

12

Naked Single

Place 6 at r2c2 - it's the only possibility for this cell.

Sudoku grid illustrating step 12: Naked Single — Place 6 at r2c2 - it's the only possibility for this cell.

13

Result after applying the technique.

Sudoku grid showing the result after applying the technique

Tips & Patterns

Pencilmarks are essential for spotting Naked Singles.
After placing any digit, check its row, column, and block for new Naked Singles.
In easy puzzles, Naked Singles can chain together quickly.