Do I need to be good at maths to solve Sudoku?

No. In Sudoku the numbers 1 to 9 are only labels. You never add, subtract or multiply. The one exception on this site is Calcudoku, where each group of squares has a total to reach.

Is it cheating to write small numbers in the squares?

No. Small notes, often called pencil marks or candidates, are a normal part of solving that many experienced players use. On paper, use a soft pencil so you can rub them out.

Should I ever guess on a Sudoku?

Not on a well-made puzzle. Every puzzle on this site has exactly one solution and can be solved by reasoning. A wrong guess often shows up many moves later. If you cannot see a move, scan again or press Hint.

Which Sudoku is the easiest place to start?

The free Easy Classic Sudoku can be finished with the two simple moves in this guide. The 6 by 6 size, which will be part of membership, is smaller still.

What does the Hint button do on this site?

The first press highlights a row, column or box where a move is waiting. The second press fills the number in. Hints only change the stars you earn at the end. They never change your time or take anything away.

How to solve Sudoku: a step-by-step beginner guide

Last updated October 1, 2026

Sudoku looks like a maths puzzle, but it uses no arithmetic. The numbers 1 to 9 are just nine symbols, and the game is keeping track of which ones are still possible where. This guide goes from the rules to the two simple moves that finish every Easy and Medium puzzle on this site. To try as you read, today’s free Easy Sudoku is one tap away.

The rules in one minute

A standard Sudoku is a grid of 81 squares, nine across and nine down, split into nine boxes of 3 by 3. Some squares already hold a number. Fill in the rest so that every row, column and box contains the numbers 1 to 9 exactly once. A well-made puzzle has exactly one answer, so you never have to guess, and a program checks every puzzle on this site to make sure.

A Sudoku with a question mark in the middle square. That square belongs to three groups: its row (shaded across), its column (shaded down) and its 3 by 3 box (the shaded middle block). Each group holds 1 to 9 once, so no number already in a shaded square can go in the middle square.

Step 1: look at the whole grid first

Before you write anything, scan by number. Pick a number that appears many times, such as 7. Each 7 rules out its whole row, column and box for any other 7. Find a box with no 7 yet and see which empty squares are not blocked by a 7 elsewhere. If only one is left, the 7 goes there. Then try 8, then 9, and go round again.

Step 2: use the two moves that solve most puzzles

There are only two ideas to learn. The Hint button on this site looks for these same two moves, so anything it does, you can learn to do yourself.

Move A: a square with only one choice

Look at an empty square and ask which numbers could still go there. Cross off every number in its row, column and box. If eight of the nine are crossed off, the ninth goes in. Experts call this a naked single.

Here the square with the question mark is in row 8, column 8. Row 8 holds 4, 1, 9 and 5. Column 8 holds 6, 8 and 7. The bottom-right box holds 2, 8, 5, 7 and 9. Together that is 1, 2, 4, 5, 6, 7, 8 and 9. Only 3 is missing, so 3 goes in the square.

Move B: a number with only one place to go

Now turn it around. Pick a box, row or column and a number that is not in it yet, and ask where that number could go. If every square but one is blocked, it goes in the last one. Experts call this a hidden single. It is the scanning from Step 1, written as a rule.

Where can a 5 go in the shaded top-right box? The circled 5 in row 1 rules out the box’s top row and the circled 5 in row 2 rules out its second row (crossed squares). In the third row one square holds a 6, and the circled 5 low in the right-hand column rules out the last. Only the first square of the third row is left, so the 5 goes there.

Step 3: keep track of what is still possible

When no move jumps out, write small notes: in each empty square, list the numbers that could still go there. Players call these pencil marks or candidates. A square with one note left is a naked single, and a number that appears in only one square of a row, column or box is a hidden single. On paper, use a soft pencil. The on-screen puzzles here have no notes mode, so press Hint: the first press highlights the row, column or box where a move waits, and the second fills the number in.

Step 4: what to do when you are stuck

Scan again. Every number you place changes what is possible, so a number you checked earlier may now have one place left.
Look at the row, column or box with the most numbers filled in, and see what is missing.
Press Undo or Hint without worry. Hints only change your stars, never your time.
Take a break. A fresh look often finds what a tired one missed.

Easy and Medium puzzles here can always be finished with Moves A and B. Hard puzzles need one idea more, such as a naked pair: when two squares in a group can only hold the same two numbers, cross those numbers off every other square in the group.

Common mistakes

Checking the row and column but forgetting the box.
Guessing. A wrong guess can sit unseen for many moves.
Forgetting to re-check the squares around a number you have erased.

Other kinds of Sudoku on this site

The 6 by 6 size uses the numbers 1 to 6. Each box is 2 squares tall and 3 wide, and every row, column and box holds each number once.
Wordoku has the classic rules with letters instead of numbers, and in each puzzle the letters spell a word.
Calcudoku (target sums) has no boxes. Heavy lines divide the grid into cages, and the small number in a cage is the total its numbers must add up to. Every row and column holds each number once.
Colorku uses bold coloured shapes instead of numbers, with the classic rules.

The free puzzle each day is the 9 by 9 Easy of each kind. The 6 by 6 sizes and the higher levels will be part of membership.

Prefer paper? free large print Sudoku printables are ready to print.

More guides

Keep going with how to solve crossword puzzles, how to solve a cryptogram, and word search tips. Or browse all the puzzle guides.

Frequently asked questions

Do I need to be good at maths to solve Sudoku?: No. In Sudoku the numbers 1 to 9 are only labels. You never add, subtract or multiply. The one exception on this site is Calcudoku, where each group of squares has a total to reach.
Is it cheating to write small numbers in the squares?: No. Small notes, often called pencil marks or candidates, are a normal part of solving that many experienced players use. On paper, use a soft pencil so you can rub them out.
Should I ever guess on a Sudoku?: Not on a well-made puzzle. Every puzzle on this site has exactly one solution and can be solved by reasoning. A wrong guess often shows up many moves later. If you cannot see a move, scan again or press Hint.
Which Sudoku is the easiest place to start?: The free Easy Classic Sudoku can be finished with the two simple moves in this guide. The 6 by 6 size, which will be part of membership, is smaller still.
What does the Hint button do on this site?: The first press highlights a row, column or box where a move is waiting. The second press fills the number in. Hints only change the stars you earn at the end. They never change your time or take anything away.

Try it now

Put it into practice with today’s Easy Sudoku. It is free every day, with no account and no ads, and the Hint button is there if you want it.

Play today’s free Sudoku

All large print Sudoku puzzles