Sudoku Rules: The 3 Rules Every Puzzle Follows

Sudoku has three core rules: each row, each column, and each 3x3 box must contain the numbers 1-9 exactly once. This page explains those rules quickly. If you want a printable reference, use the Sudoku rules cheat sheet. If you want a full beginner walkthrough, go to How to Play Sudoku.

The 3 rules of Sudoku

1. Rule 1: Fill every row with 1–9

   Each of the nine horizontal rows must contain the digits 1 to 9 exactly once. No number can appear twice in the same row.

2. Rule 2: Fill every column with 1–9

   Each of the nine vertical columns must also contain 1 to 9 exactly once. A number already placed in a column cannot appear again in that column.

3. Rule 3: Fill every 3×3 box with 1–9

   The grid is divided into nine 3×3 boxes. Each box must contain 1 to 9 exactly once. Together, the row + column + box constraints give you everything you need to solve a puzzle logically.

How to play Sudoku step by step

1. Step 1: Look at the given numbers

   When you open a puzzle, some cells already have numbers — these are called givens and are fixed. They are your starting clues.

2. Step 2: Find a nearly complete row, column, or box

   Scan for any row, column, or 3×3 box that has 7 or 8 of its 9 numbers already placed. There are only 1 or 2 empty cells remaining, so it is easy to see which numbers are missing.

3. Step 3: Use elimination to place a number

   For any empty cell, check: which numbers are already in its row? Its column? Its 3×3 box? Any number already present in one of those three groups cannot go in that cell. If only one number is left possible, place it.

4. Step 4: Use pencil marks for harder cells

   When a cell has multiple possible values, write the candidates lightly as small notes. As you fill in surrounding cells, cross off candidates until one remains.

5. Step 5: Repeat until the grid is full

   Work through the puzzle systematically. Each number you place makes other cells easier. If you get stuck, try looking at a different part of the grid — a fresh row or box often reveals a new move.

Beginner tips

• Start with the easiest cells

  Always begin in rows, columns, or boxes with the most givens. The fewer empty cells, the easier it is to deduce the missing number.

• You never need to guess

  Every well-made Sudoku puzzle has a unique solution reachable by logic alone. If you feel forced to guess, step back — there is a clue you have not spotted yet.

• Check all three groups before placing

  Before writing a number, quickly verify it does not already appear in the same row, column, or 3×3 box. This habit prevents most beginner errors.

Learn more

Sudoku rules FAQ