---
title: "Hidden Single: Sudoku Technique #4 | Sudoku Flow"
description: "Hidden Single: If a number is a candidate in only one cell of a row, column, or box, it must go there even if that cell has other candidates."
url: https://sudokuflow.com/lessons/hiddenSingle/
language: en
---

[Sudoku technique lessons](https://sudokuflow.com/lessons/) / Hidden Single

Lesson 4

# Hidden Single

## The rule

If a number is a candidate in only one cell of a row, column, or box, it must go there even if that cell has other candidates.

## Step by step

1. The number 1 is missing from this row. Let's see where it can go.
2. The other empty cells in this row are each blocked from taking 1, so remove the candidate 1 from them.
3. Now only one cell in this row still has the candidate 1, so it must go here.

[Read the full lesson, with more examples →](https://sudoku.rubigogames.com/techniques/hidden-single.html) [Watch on YouTube](https://youtube.com/shorts/KlFE-VwOdTM)

In our app, when this technique is the next step, the hint names it and shows you why, step by step. No ads, free to download.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_cta&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dcta%26utm_campaign%3Dlesson)

## Try it on more boards

Each board is a real puzzle from our app, at a moment where Hidden Single applies. Find the step yourself, or tap Hint and the app's own hint walks you through it.

Hidden Single practice board:

```text
.  8  .  | 1  4* .  | 2  .  .
4  1* .  | .  7  .  | .  8  5
2* .  6  | 9  5* 8* | .  1* .
---------+----------+---------
8* 5* 2* | 4  1* 9  | 3  6  7*
1  .  .  | .  6* .  | .  5  .
7  6* .  | .  3  .  | .  .  .
---------+----------+---------
.  .  .  | .  2* .  | .  4  1
3  4* .  | 6  9* 1  | 5  .  .
.  2  1* | .  8  4* | .  3  .
```
Digits marked * were filled in by a player; the others were printed with the puzzle.

![Sudoku app icon](https://sudokuflow.com/assets/app-icon.png)

## Want more boards like this?

We also make a Sudoku app for iPhone, iPad, Mac and Android. There are no ads in it at all, it works offline, and when you ask for a hint it shows you the technique instead of just filling in a number.

[App Store iPhone, iPad, Mac](https://apps.apple.com/app/apple-store/id6502922368?pt=125379530&ct=sudokuflow_web&mt=8) [Google Play Android](https://play.google.com/store/apps/details?id=com.rubigogames.sudoku&referrer=utm_source%3Dsudokuflow%26utm_medium%3Dweb%26utm_campaign%3Dsite)

Sudoku Flow is made by Rubigo Games, the developer of the Sudoku app recommended on this site.