Intermediate
Hidden Singles
A core Sudoku solving technique for intermediate players
What are Hidden Singles?
A Hidden Single is a cell where a particular digit can only go in one position within a unit - Even though that cell appears to have multiple candidates. The digit is "hidden" among other candidates, but when you scan the unit for where that digit can go, only one cell is legal.
While Obvious Singles are found by looking at cells (which cell has only one candidate?), Hidden Singles are found by looking at digits (which digit has only one possible cell in this unit?).
Step-by-step guide
- Fill in candidate notes for all empty cells.
- Pick a unit (a row, column, or box) and a digit not yet placed in that unit.
- Highlight every cell in the unit where that digit appears as a candidate.
- If only one cell is highlighted, that cell must contain that digit - Place it.
- Repeat for every digit in every unit.
How common are Hidden Singles?
Approximate % of puzzles where Hidden Singles are required to progress.
Stuck on Medium? Hidden Singles are the most common reason players get stuck moving from Easy to Medium. Switching your scan from "look at cells" to "look at digits" is the single biggest skill jump in beginner Sudoku.