The Hidden Single in Sudoku
The Hidden Single is the technique that turns a “stuck” grid back into a solvable one. When a digit can go in only one cell of a row, column or box, it must go there — even if that cell still shows other candidates. It is the most-missed beginner move, and learning to see it is the single biggest jump in solving speed.
How to use Hidden Singles, step by step
- Pick a digit and a unit — a row, column or box.
- Check every cell in that unit where the digit could still legally go.
- If there is exactly one such cell, the digit must go there.
- Place it, even if the cell also showed other candidates.
- Sweep digit by digit and unit by unit to find them all.
What is a Hidden Single?
A Hidden Single is a digit that has only one possible home within a unit, so it claims that cell — regardless of the cell’s other candidates. It is “hidden” because the cell does not look special; only by tracking the digit do you see it has nowhere else to go. It is the counterpart of the Naked Single.
Why Hidden Singles matter most
Most grids that feel impossible are hiding a Hidden Single in plain sight. Solvers who only hunt Naked Singles get stuck; those who also ask “where can this digit go in this box?” keep moving. Work one digit at a time across the boxes — it is the fastest way to surface them. More in tips & strategy.
Hidden Single in Sudoku: FAQ
What is a Hidden Single in Sudoku?
A Hidden Single is a digit that can be placed in only one cell of a given row, column or box. It must go there, even if that cell still lists other candidate digits.
How do you find Hidden Singles?
Work one digit at a time. For each box, row or column, check where that digit can still go; if there is only one legal cell, place it there. Scanning digit by digit is the most reliable method.
Why are Hidden Singles easy to miss?
Because the cell often still shows several candidates, so it does not look forced. You only see the move by tracking where a digit can go, not what a cell can be.