Naked Single in Sudoku

A Naked Single is a cell whose candidate list has shrunk to a single number. Because every cell must hold something, and everything else has been ruled out by its row, column and box, that number goes in. It is the most common move in Sudoku and the one every other technique is ultimately trying to create.

Also known as: Sole Candidate, Forced Digit.

Download on theApp Store Get it onGoogle Play

Why it works

A cell with only one candidate left must hold that number.

How to spot it

Naked Singles are easy to miss without notes and nearly automatic with them. If you are solving on paper, the scan is: pick an empty cell, run through 1 to 9, and stop early the moment you find two numbers that still fit.

Cells in a busy box, crossed by two well-filled lines, are where they appear first.
Every number you place can create a new Naked Single in the 20 cells it sees, so check those before looking anywhere else.
In the app, turn on notes and the single-candidate cells stand out on their own.

Builds on

Last Remaining Cell

Worked example

These are the app's own lesson boards. Step through them the same way a hint does.

PatternAnswerContextBlockerElimination

125679

3

4

8

1

6

2

7

9

Step 1 of 4

Naked Single: the pattern as the app draws it during a hint.

1
Look at this row. It already contains 3, 4, 8.
2
Now check this column. It also contains 2, 7, 9.
3
The box also contains 1, 6, so remove those candidates from this cell.
4
All other candidates are eliminated! Only 5 can go in this cell.

Where it fits

The game looks for the easiest technique that applies before it offers you a harder one. Naked Single sits at position 3 of 37 on that ladder, which is why puzzles that need it are graded Easy.

Learn before thisNearly Complete Learn after thisHidden Single

Other Easy techniques

Last Remaining Cell Nearly Complete