Learn Sudoku

How to Play Sudoku: A Beginner's Guide

CalmSudoku GuideUpdated August 27, 2026

Sudoku is logic, not arithmetic

Sudoku uses numbers, but you do not need to calculate anything. A standard puzzle is a 9x9 grid divided into nine 3x3 boxes. Some cells already contain numbers, called givens, and your job is to fill the empty cells using logic. Every completed puzzle uses the digits 1 through 9 repeatedly, but each digit has strict placement rules.

The three rules you need to know

Every row must contain the numbers 1 through 9 exactly once. Every column must also contain 1 through 9 exactly once. Finally, every 3x3 box must contain 1 through 9 exactly once. A number therefore cannot be placed in a cell if the same number already appears in that cell's row, column, or box.

How to make your first move

Start with a row, column, or box that already contains many numbers. Ask which digits are missing. Then inspect each empty cell and eliminate any missing digit that conflicts with its row, column, or box. If only one digit can legally fit a cell, you have found a safe move. This is often called a naked single.

Look for a number that has only one place

Sometimes an empty cell still has several possible digits, but one particular digit can appear in only one cell within a row, column, or 3x3 box. That placement is forced even though the cell itself has several candidates. Solvers commonly call this a hidden single.

Use Notes when the answer is not obvious

CalmSudoku's Notes mode lets you record candidate digits without committing to an answer. For example, if an empty cell could currently be either 2 or 7, note both possibilities. As you solve nearby cells, one candidate may be eliminated. Notes are especially useful as difficulty increases because they turn uncertainty into visible information you can reason about.

A simple beginner solving routine

Scan one 3x3 box at a time, then scan rows and columns. Fill obvious singles first. Re-scan after every few placements because each new number can create another forced move. If you become stuck, add candidate notes instead of guessing. Sudoku is a chain of deductions: one correct placement often unlocks several more.

What happens if you make a mistake?

A wrong entry does not mean you are bad at Sudoku. It usually means a row, column, or box was not checked carefully enough. Slow down and verify all three before committing. On CalmSudoku you can use Undo and Erase, so the useful goal is to understand why a number belongs in a cell rather than racing through the board.

Ready to play?

Choose Beginner or Easy on CalmSudoku and practice the process immediately. The game is free, requires no registration, and includes optional live music if you prefer background audio while solving. Once singles begin to feel automatic, move to Medium and start using candidate notes more deliberately.