The Naked Single is the most fundamental Sudoku technique. When a cell has only one possible number remaining, that number must be the answer.
A Naked Single occurs when you examine an empty cell and determine that only one number from 1 to 9 can possibly go there. You reach this conclusion by checking which numbers are already placed in the cell's row, column, and 3x3 box. If eight of the nine possible numbers are already accounted for, the remaining number is the only candidate - making it a Naked Single.
The term "naked" refers to the fact that the single candidate is fully exposed - there is no ambiguity. Unlike Hidden Singles, where you need to look at the broader context of a row, column, or box, a Naked Single is determined entirely by the candidates available in one specific cell.
This technique is sometimes also called a "Sole Candidate" or "Forced Cell" in various Sudoku resources. You can learn more about Sudoku terminology in our Sudoku glossary.
Naked Singles should be your very first approach on every puzzle, regardless of difficulty. They appear frequently in easy Sudoku puzzles, where many cells are pre-filled, creating numerous Naked Singles from the start. In medium and hard puzzles, Naked Singles become more common as you fill in cells using other techniques - each placement may reveal new Naked Singles in connected cells.
If you are new to Sudoku, we recommend starting with our how to play Sudoku guide to understand the basic rules before applying strategies. You can also explore our complete list of Sudoku strategies to see how Naked Singles fit into the bigger picture of Sudoku solving.
Naked Singles is classified as a beginner-level technique. It is the easiest strategy to learn and the first one you should master. Here is how it applies across puzzle difficulties:
Very frequent - many puzzles can be largely solved with singles alone
Frequent - singles appear after applying pairs and other techniques
Moderate - often revealed as a byproduct of advanced eliminations
Occasional - still essential as a finishing technique after complex moves
A Naked Single occurs when a cell in the Sudoku grid has only one possible candidate remaining after eliminating all numbers already present in its row, column, and box. It is the most basic and fundamental solving technique.
Scan each empty cell and mentally or physically note which numbers 1-9 are already used in its row, column, and box. If only one number is left, that cell is a Naked Single. Many solvers use pencil marks to track candidates and spot singles faster.
Not exactly. A Full House is a special case where a row, column, or box has only one empty cell remaining, making the answer obvious. A Naked Single is broader - it applies to any cell with one candidate, even when many cells in its row, column, and box are still empty.
Most easy puzzles can be solved using a combination of Naked Singles and Hidden Singles. Some very simple puzzles can be completed with Naked Singles alone, but you will usually need Hidden Singles as well to fully solve even easy-rated puzzles.
After Naked Singles, learn Hidden Singles - the other essential beginner technique. Together, these two strategies form the foundation for all Sudoku solving. From there, progress to Naked Pairs and Pointing Pairs for intermediate puzzles.
Look at the highlighted cell. What number can fit there?
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