How to Play Sudoku: Rules and a Step-by-Step Guide for Beginners
Sudoku looks intimidating the first time you see a half-empty 9×9 grid, but the rules fit in three sentences and the first moves follow directly from them. This guide explains how to play Sudoku step by step: what the grid is, what the rules say, how to find your first digits, and which habits turn a slow beginner into a confident solver. The board above is set to Easy so you can try each step as you read.
The Sudoku grid
A standard Sudoku is a 9×9 grid of 81 cells. Bold lines divide it into nine 3×3 boxes (also called blocks or regions). Some cells already contain digits; these are the givens. An Easy puzzle here starts with 38 givens, an Extreme puzzle with as few as 22. Your job is to fill the empty cells.
Sudoku rules explained
- Every row must contain each digit from 1 to 9 exactly once.
- Every column must contain each digit from 1 to 9 exactly once.
- Every 3×3 box must contain each digit from 1 to 9 exactly once.
That is the whole rulebook. There is no arithmetic and the digits never add up to anything; they are simply nine different symbols. A properly made puzzle has exactly one solution, so every empty cell has one correct answer that can be reached by logic. Guessing is never required and, with the mistake limit on, costs a life.
How to play Sudoku step by step
Step 1: Look for nearly complete rows, columns and boxes
Any unit with eight digits filled tells you the ninth immediately: it is whichever digit is missing. Scan the grid for these first. On Easy boards there are usually two or three.
Step 2: Pick a digit and find where it must go
Choose a digit that already appears often, say 5. Take a box that has no 5 yet. Every 5 elsewhere on the board blocks its entire row and column, and those lines cut through the box. If only one cell in the box escapes every line, the 5 belongs there. Repeat for the other boxes, then for the other digits.
Step 3: Pick a cell and rule out what it cannot be
Now do the reverse. Choose an empty cell and list every digit already present in its row, its column and its box. If eight different digits are taken, the cell must be the ninth. Cells in crowded areas of the grid are the best candidates.
Step 4: Re-check around every digit you place
Each placement removes a possibility from up to twenty other cells. After every move, look again at the row, column and box you just changed; a new "last cell" or "only place" usually appears nearby.
Step 5: Use notes when the obvious moves run out
On Medium and harder boards you will reach a point where no cell is decided by steps 1 to 3 alone. Switch on Notes and write the remaining candidates into the empty cells. A cell with a single note is a naked single; a digit that appears in only one cell's notes within a unit is a hidden single. Both can be placed. Our Sudoku techniques guide takes it from there.
Common beginner mistakes
- Guessing early. A guess that happens to work teaches nothing, and one that fails can poison the rest of the grid. Logic always has a next move.
- Forgetting the box. New players check the row and column and miss that the digit already sits in the 3×3 box.
- Sloppy notes. A candidate you forgot to write creates a false single later. Be complete or do not write notes for that cell at all.
- Staring at one region. If a corner will not move, leave it. Placements elsewhere will unlock it.
Using this site's controls
Click or tap a cell, then choose a digit from the pad or press 1 to 9 on the keyboard. The row, column and box of the selected cell are shaded and every copy of the selected digit is highlighted, which makes the scanning in steps 2 and 3 much faster. Wrong entries turn red at once and must be fixed before you continue. You get three hints per puzzle, unlimited undo, a timer you can switch off in Settings, and your game saves itself so you can come back later.
How to practise
Play Easy Sudoku until finishing one feels routine, then move to Medium, where hidden singles become necessary. When Medium feels routine too, move on to Hard. The difficulty levels guide explains exactly what changes at each step.
Frequently asked questions
What are the rules of Sudoku?
Fill the 9×9 grid so that every row, every column and every 3×3 box contains the digits 1 to 9 exactly once. The digits printed at the start cannot be changed.
Is Sudoku a math game?
No. Nothing is added, subtracted or multiplied. The digits are just nine distinct symbols, and the puzzle would work exactly the same with letters or colours. Sudoku trains logic and pattern recognition, not arithmetic.
Where should a beginner start on a Sudoku grid?
With the most crowded areas: rows, columns and boxes that already hold six or more digits, and the digits that appear most often on the board. Those are where the first forced placements hide.
Do I ever need to guess in Sudoku?
Not in a well-made puzzle. Every board on this site is verified to have a single solution, so a logical next step always exists. If you feel stuck, switch viewpoints from cells to digits or turn on notes.
How long does it take to learn Sudoku?
The rules take a minute to read. After that it is practice: move from Easy to Medium when Easy feels routine, and on to Hard when Medium does. How long that takes varies a lot from person to person.