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
Look at one empty square. Every digit already in its row, column or box is ruled out. If just one digit remains, it belongs there. That is a Naked Single.
How to spot it
Start with empty squares in busy rows, columns or boxes. Ask only: which digit is still missing here? If one digit remains after crossing off the visible ones, place it. Notes can help, but you do not need them.
Worked example
One question at a time: watch the marked square, then click Next.
Step 1 of 4: Look at the marked square
Do not calculate anything yet. This square will end with exactly one digit.
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.
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