Naked Single
A cell where only one digit still fits. The most direct move in Sudoku, and the one every other technique is ultimately trying to create.
What it is
A naked single is an empty cell whose row, column and box between them already contain eight of the nine digits. Exactly one candidate survives, so that digit belongs in the cell — no further reasoning required. It is called “naked” because the answer is visible in the cell itself rather than hidden in the surrounding unit.
How to spot it
Look for empty cells in crowded areas: a row with seven or eight filled cells, or a box that is nearly complete. Cross off the digits already present in the cell's row, column and box. If exactly one remains, you have found a naked single. Pencil marks make these obvious, which is why turning on notes speeds up beginners so much.
Worked example
Step through the reasoning below. Each step adds one layer: first the position, then the pattern, then the candidates involved, and finally what can be eliminated.
Step 1 of 3: The starting position
- Pattern cells
- 2/8
- Digits
- 5
- Eliminations
- —
Press a marked square to point it out on the board above.
Why it matters
Every solve ends in naked singles. Advanced techniques do not fill cells directly; they remove candidates until a naked single appears. Recognising them quickly is what turns a slow grind into a smooth solve, and it costs nothing in effort once you read pencil marks fluently.
Practise now
Solve a puzzle where this technique decides the game
Frequently asked questions
What is the difference between a naked single and a hidden single?
A naked single is about the cell: only one digit fits there. A hidden single is about the digit: it fits in only one cell of a row, column or box, even though that cell may have several candidates. Naked singles are found by looking at cells, hidden singles by looking at digits.
Do I need pencil marks to find naked singles?
No, but they help enormously. Without notes you must mentally scan the row, column and box for each empty cell. With notes the single candidate is written in front of you. Most solvers use notes on medium difficulty and above.
Why does my puzzle have no naked singles left?
That is normal on harder puzzles. It means you need an elimination technique first — a naked pair, a pointing pair or something stronger — to remove candidates until a cell is reduced to one. The naked single is the reward, not the method.
Put it to use
Where you will meet it
This pattern is the backbone of easy grids. Start one and you will use it within a few moves.
Play EasyStuck on a grid of your own?
Type the position into the solver and it walks the whole solution, naming the technique behind every step — including this one.
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