A hidden single occurs when a candidate can only fit in one cell within a unit (row, column, or 3x3 block), even if that cell still shows other possible candidates. This is different from a naked single, where a cell has only one candidate remaining.

Hidden singles are one of the most important [Sudoku strategies](https://sudokubliss.com/guides/sudoku-tips-and-strategies) for beginners. They appear in nearly every easy or medium-level Sudoku puzzle and are often the key to making steady progress. By identifying them early and often, you can place numbers confidently and build a foundation for more advanced techniques, such as hidden pairs, when you [play Sudoku](https://sudokubliss.com/).

## How to Find Hidden Singles

Hidden singles must meet the following criteria:

* The candidate number can only appear in one cell within a row, column, or 3x3 block.
* The cell must contain other candidates, effectively “hiding” the single candidate.
* That number is not a valid candidate in any other cell within the unit.
![Example of finding hidden singles in a Sudoku puzzle](https://sudokubliss.com/content-uploads/how-to-find-hidden-singles-Sudoku-example.webp)  

To find hidden singles, follow these simple steps:

1. **Note all possible candidate numbers in each cell.** You can analyze cells and place pencil marks in them by turning on candidate mode (check the box next to “This number is a possibility”) or quickly populate each cell’s possibilities by clicking the “Show Possibilities” button.
2. **Find a candidate that only appears once in a row, column, or block, even if that cell contains other candidates.** For example, when looking at row 1, you can see that 8 only appears in cell H1, even though H1 has multiple candidates.
3. **Confirm it cannot be placed elsewhere in the unit.** If a number can only go in one cell within that unit, it must be placed there, even if that number appears as a candidate in intersecting units. For example, 8 cannot be placed anywhere else in row 1.
4. **Place the hidden single.** Because 8 only appears in H1 for that row, it must be the answer for that specific cell (H1).

Hidden singles often appear after placing a number and updating candidates, so make sure to rescan units for new hidden singles regularly.

## Hidden Single Examples

Although many consider it a basic technique, finding a hidden single can create a chain reaction of placements. So using this simple Sudoku strategy can often unlock a puzzle quickly and level up your puzzle-solving skills if you can find hidden singles in rows, columns, and blocks.

### Hidden Singles in a Row

To find a hidden single in a row:

1. **Note all possible candidate numbers in the grid.** Click the “Show Possibilities” button to do this in one move or add pencil marks using candidate mode.
2. **Look for a candidate that only appears once in a row of the puzzle, even if that cell contains other candidates.** For example, when looking at row 4, you can see that 3 only appears in cell D4.
3. **Confirm it cannot be placed elsewhere in the row.** Candidate 3 is not a valid placement for any other cell in that row (4).
4. **Place the hidden single.** Because 3 only appears in D4 for that row, it must be the answer.
![Example of hidden singles in a row](https://sudokubliss.com/content-uploads/hidden-singles-in-a-row-example.webp)  

### Hidden Singles in a Column

To find a hidden single in a column:

1. **Note all possible candidate numbers in the grid.** Click the “Show Possibilities” button or add your own pencil marks using candidate mode.
2. **Look for a candidate that only appears once in a column of the puzzle, even if that cell contains other candidates.** For example, when looking at column C, you can see that 4 only appears in C5 and 3 only appears in cell C7.
3. **Confirm it cannot be placed elsewhere in the column.** Candidates 3 and 4 don’t appear in any other cells in column C.
4. **Place the hidden single.** In this column, 4 can only go in C5 and 3 can only go in C7, so place them there, then remove those numbers as candidates from intersecting units.
![Example of hidden singles in a column](https://sudokubliss.com/content-uploads/hidden-singles-in-a-column-example.webp)  

### Hidden Singles in a Block

To find a hidden single in a block:

1. **Note all possible candidate numbers in the grid.** You can view them by clicking the “Show Possibilities” button or by adding pencil marks with candidate mode.
2. **Look for a candidate that only appears once in a block of the puzzle, even if that cell contains other candidates.** For example, when looking at the bottom-right block, you can see that 1 only appears in cell G7.
3. **Confirm it cannot be placed elsewhere in the block.** No other cell in the block has 1 as a candidate.
4. **Place the hidden single.** Because 1 only appears in G7 for that block, it must be the answer and can be placed in that cell.
![Example of hidden singles in a block](https://sudokubliss.com/content-uploads/hidden-singles-in-a-block-example.webp)  

Finding and placing hidden singles is a reliable solving technique that can create a cascade of placements, allowing you to move quickly through [easy Sudoku puzzles](https://sudokubliss.com/easy). When done proficiently, you can elevate your Sudoku solving skills and try harder puzzles and more advanced techniques when you play [Sudoku online](https://sudokubliss.com/).