---
title: "How to play Sudoku: rules and your first move"
description: "One of each number in every row, column and 3×3 box: learn the rules of classic Sudoku and follow a first certain move."
lang: "en"
canonical: "https://unisu-sudoku.app/en/sudoku-rules/"
---

[Back to the learning guides](https://unisu-sudoku.app/en/learn/)

Fundamentals

# How to play Sudoku: rules and your first move

One of each number in every row, column and 3×3 box: learn the rules of classic Sudoku and follow a first certain move.

![Unisu lesson on Full House, showing the explained grid](https://unisu-sudoku.app/_astro/en.Bnh-GLbv_INnQn.webp)

Sudoku is a logic puzzle. The digits 1 to 9 are symbols for different possibilities. You don’t need arithmetic to solve it.

## The three rules

Fill the 9×9 grid so that each digit from 1 to 9 appears exactly once in every row, every column and each of the nine 3×3 boxes. The given numbers stay fixed. A move must respect all three areas around its cell.

## A row with one gap

The first row in the example reads 5, 3, 4, 6, a gap, 8, 9, 1 and 2. The only missing digit is 7, so it belongs in the fifth cell. This situation is called Full House.

A second 5 would break the row rule. When several cells are empty, a number missing from the row is not enough to decide where it goes: check each cell’s column and box as well.

## What comes next?

Look for other rows, columns and boxes with one gap. Where several possibilities remain, pencil marks and the two single techniques help you reason further. There is no need to memorize a complete solution path.

## Frequently asked questions

### Do the diagonals need every digit too?

Classic Sudoku applies the rules to rows, columns and 3×3 boxes. Diagonals are not additional areas that must contain each digit once.

### Do I need arithmetic to play Sudoku?

No. The digits represent nine different values. You reason about which values are present and which positions remain possible.

### Can I change the given digits?

The givens belong to the puzzle and stay fixed. Fill the empty cells while respecting all three rules.

### Where should I start on an almost full grid?

Look for a row, column or box with one empty cell. Its one missing digit already has a fixed place.

### What if several digits are still possible?

Note the allowed candidates and examine the other areas. A possibility is not yet a justified placement.

## Keep practicing in Unisu

Download Unisu for iPhone or Android. Solve a puzzle or work through a guided lesson on the technique.

-   [Download on the App Store](https://apps.apple.com/us/app/id6775824061?l=en)
-   [Get it on Google Play](https://play.google.com/store/apps/details?id=app.unisu.sudoku&hl=en)

## Where to go next

Fundamentals

Unisu · Oct 27, 2026

### [Full House: One gap, one missing digit](https://unisu-sudoku.app/en/sudoku-techniques/full-house/)

A Full House has just one empty cell in a row, column or 3×3 box. The one missing digit belongs in that cell.

Unisu

### [Learn Sudoku: a path from rules to techniques – Unisu](https://unisu-sudoku.app/en/learn/)

Start with the rules, get comfortable with pencil marks and choose a technique for the situation you’re working on.

Download app

## Ready for a puzzle? Take a moment.

Download Unisu on your phone. Start a Sudoku or choose a lesson on the technique you want to understand.

-   [Download on the App Store](https://apps.apple.com/us/app/id6775824061?l=en)
-   [Get it on Google Play](https://play.google.com/store/apps/details?id=app.unisu.sudoku&hl=en)

![The daily challenge in Unisu](https://unisu-sudoku.app/_astro/en.C-sYR9hJ_1QwI9G.webp)

![A classic Sudoku game in Unisu](https://unisu-sudoku.app/_astro/en.C6DJ1kiE_2dRWDN.webp)