How to solve sudoku, with tips
New to sudoku? Start with "The rules" and "A worked example". If you get stuck partway, go to "Finding the next move". Every figure is a board from a real puzzle. To solve on paper, there are printable sudoku too (2,000 puzzles, with answers). The pages for printing, the levels and the step-by-step examples linked here are in Japanese, but the boards read the same in any language.
Play sudoku free →1What is sudoku?
Sudoku is a logic puzzle: you fill a 9×9 grid with the digits 1 to 9. It is a favourite in magazines and newspapers around the world. The only question is "where does this digit go?", so it suits everyone, from schoolchildren to grandparents.
Sudoku and Nanpure
In Japan, where the puzzle got its name, sudoku is usually called Nanpure, short for "Number Place". "Sudoku" is a registered trademark there of the puzzle maker Nikoli, so other publishers and magazines use Nanpure. It is the same puzzle, with the same rules.
2The rules
You fill a 9×9 grid with the digits 1 to 9. There is just one rule:
- Every row, every column and every 3×3 box outlined in bold holds each digit 1 to 9 exactly once.
The digits already on the board at the start are the clues, and they cannot be moved. The digits are only symbols: you never add or subtract them. A well-made puzzle has exactly one answer.
3New to sudoku: how a solve goes
- Look where there are many digits. Start with the rows, columns and boxes that are already well filled. The more clues, the easier a cell is to decide.
- Follow one digit. Say you pick 1: see where the 1s are on the board. Then, in a box that has no 1 yet, look for the cell where a 1 can go (method 1 in "The two basic ways to solve" below). Digits that appear often on the board are the easiest to follow.
- Write it when it is certain; make a note when it is not. If only one cell is possible, write the digit in. If there are several candidates, jot them small in the corner of the cell.
- Repeat. Every digit you place gives you more clues. Repeating these two ways of looking (in "The two basic ways to solve" below) solves an Easy puzzle to the end.
Starting straight away with a hard puzzle often leads to getting stuck. Try an Easy puzzle first.
To teach young children, begin with 6×6 sudoku, which uses only the digits 1 to 6: the rule comes across at once. At first, teaching "where does this digit go?" (the hidden single, below) is enough.
4A worked example: the first ten moves
Let's follow the first ten moves of a real puzzle: printable Easy No.3. Print it and solve along with us. Cells are named by row and column: "row 6, column 7" is the sixth row from the top and the seventh column from the left.
Move 1: start where the digits are
The top three rows (rows 1 to 3) are already well filled. With so many clues, that is where we start. The top-left box has three empty cells. Where can the 4 go?
Rows 1 and 2 already have a 4 (the shaded rows). So in the top-left box, the 4 can only go in the empty cell in row 3.
Moves 2 and 3: the rest of the same box
The top-left box has two empty cells left, and the digits still missing are 2 and 7. Row 2 already has a 2, so the 2 goes in the row 1 cell. The last cell is 7.
Row 2 already has a 2, so the 2 goes in the row 1 cell. Blue digits are the ones placed in earlier moves.
Moves 4 to 9: from the top three rows to the middle
The same way of looking decides one cell at a time. Each digit you place makes its row and column a new clue.
- Moves 4 and 5, the top middle box (6 and 8): two empty cells. Row 1 already has a 6, so the 6 goes in row 2 and the 8 in row 1.
- Moves 6 and 7, the top-right box (1 and 2): two empty cells. Row 3 already has a 1, so the 1 goes in row 1 and the 2 in row 3. The top three rows are now complete.
- Move 8, the 5 in the centre box: rows 4 and 6 and column 6 already have a 5, so the only place is row 5, column 4.
- Move 9, the 7 in the middle-right box: rows 5 and 6 and column 9 already have a 7, so the only place is row 4, column 8.
Move 10: a cell with only one possible digit
Now look at the cell in row 6, column 7. Its row, column and box already hold every digit except 8. So this cell is 8.
The row, column and box of row 6, column 7 (the shaded cells) hold every digit except 8.
From here on, these two ways of looking solve the rest of the puzzle. The answer is on the second page of the printable sheet.
5The two basic ways to solve
1. Find where a digit can go (hidden single)
Pick one box (or row, or column) and ask "where does this digit go?". A digit cannot go in a cell whose row or column already has it, so rule those cells out. Sometimes only one cell is left. See it step by step →
In the top-left box, the 5 has only one place. Rows 1 and 3 and column 3 already have a 5, and the second cell of row 2 is filled.
2. Narrow down what a cell can hold (naked single)
This time, pick one cell. No digit already in its row, column or box can go there, so rule those out. If eight different digits are there, the cell can only be the one left. See it step by step →
The centre cell can only be 7. Its row, column and box (the shaded cells) hold the other eight digits.
6Using notes
In harder puzzles, you run out of cells that are easy to decide. Then write small notes in each cell: the digits that could still go there (its candidates).
- When you place a digit, erase it from the notes in the same row, column and box.
- A cell left with one candidate is that digit.
- In the Puzzle Lounge's sudoku you can write notes one at a time, or fill in the candidates of every empty cell at once.
- Writing a digit clears it from the notes in the same row, column and box for you.
After writing 7 in the sixth cell, erase the 7s from the notes in the same row (red). Erase them from the same column and box too.
With notes, the "Advanced techniques" below become possible.
7Finding the next move
When you are stuck, go over the board in this order. The first ones are the easiest to spot. As soon as you find something, place the digit and start again from the top.
- Go through the boxes digit by digit. For each digit from 1 to 9, look for a box without it where it has only one place (hidden single).
- A cell with one candidate. If you have notes, look for a cell with only one candidate left (naked single).
- Candidates in a line inside a box. In a box, see whether a digit's candidates all lie in the same row or column (pointing).
- Cells with only two candidates. Look for two cells in the same row, column or box with exactly the same two candidates (pairs). If two digits can only go in the same two cells, that is a hidden pair. Three two-candidate cells apart from each other may form an XY-Wing.
- A digit with only two places. In a row (or column), look for a digit that can go in only two cells. Two such rows whose columns line up make an X-Wing.
If you still find nothing, suspect a note you forgot to erase. It is common to place a digit and not remove it from the notes in its row, column and box. Putting in a digit on a hunch (guessing) is not a good idea: you notice the mistake late and have to go back a long way. On screen, press Hint instead. It shows you where to look first, then step by step.
8Advanced techniques
From here on, the ideas do not place digits: they remove candidates. As candidates go, cells that can be decided appear again. Below, two cells "see" each other when they share a row, column or box.
Worked examples on real boards (in Japanese): pointing, claiming, pairs, triples, hidden pairs, hidden triples, X-Wing, Swordfish, XY-Wing. Techniques for Master: Skyscraper, Two-String Kite, XYZ-Wing, W-Wing, Jellyfish.
Pointing (a line inside a box)Medium and up
Sometimes, inside a box, a digit's candidates all lie in one line (the same row or the same column). Then that digit must go somewhere on that line within this box. So it can be removed from the cells of the same line outside the box. Example →
The top three rows, with only the 4s' candidates written. In the top-left box, the 4's candidates lie only in row 2. So the 4 can be removed from the other cells of row 2 (red).
Claiming (a box inside a line)Medium and up
The other way round: in a column (or row), a digit's candidates sometimes all fall inside one box. Then that digit must go in the part of the column inside that box. So it can be removed from the other cells of the same box. Example →
Pairs and triplesHard and up
Sometimes two cells in the same row (column, box) both have the same two digits as their only candidates. If they are 3 and 7, say, then 3 and 7 are used up by these two cells. So 3 and 7 can be removed from the other cells of the row. The same idea works with three cells and three digits (a triple). Pair example → Triple example →
The second and seventh cells both have only 3 and 7. The 3s and 7s in the other cells can be removed (red).
X-WingOni
Suppose a digit's candidates, in two rows, lie only in the same two columns. Then the digit goes in opposite corners of the rectangle the two rows make. Whichever pair of corners it is, each of the two columns gets this digit once. So it can be removed from the other rows of those two columns. The same works with rows and columns swapped. Example →
Only the 8s' candidates are written. In rows 5 and 9, the 8 can only go in columns 2 and 9. Whichever corners it takes, column 2 gets its 8 there, so the 8 in row 8, column 2 can be removed (red).
SwordfishOni
The X-Wing stretched to three rows. If a digit's candidates, in three rows, all fall within the same three columns, the digit can be removed from the other rows of those three columns. Example →
XY-WingOni
Three cells with two candidates each (say AB, BC and AC) work together. When the middle cell (AB) sees both end cells (AC and BC), no cell that sees both ends can be C. Whether the middle is A or B, one of the ends becomes C. Example →
The middle cell, row 2, column 8, is 4 or 5. If it is 4, row 2, column 6 becomes 3; if 5, row 3, column 7 becomes 3. Either way a 3 goes there, so the 3 in row 3, column 5, which sees both, can be removed (red).
SkyscraperMaster
Two rows each have only two places for a digit, and one end of each lines up in the same column. The digit cannot be in both of the lined-up cells, so it must be in one of the two ends that do not line up. So it can be removed from any cell that sees both of those ends. Example →
Two-String KiteMaster
A row and a column each have only two places for a digit, and one end of each falls in the same box. The digit must be in one of the other two ends, so it can be removed from any cell that sees both of them. Example →
XYZ-WingMaster
An XY-Wing whose middle cell has three candidates (ABC). When the middle sees an AC cell and a BC cell, one of the three cells must be C. So C can be removed from any cell that sees all three. Example →
W-WingMaster
Two cells apart from each other have the same candidates, AB. A row (column, box) has only two places for A, and each of those two places is seen by one of the two cells. One of the two cells must be B, so B can be removed from any cell that sees both. Example →
JellyfishMaster
The Swordfish stretched to four rows. If a digit's candidates, in four rows, all fall within the same four columns, the digit can be removed from the other rows of those four columns. Example →
9Tips for solving faster
- Look at three boxes side by side at once. If a digit is in two of three boxes in a band, the third box has only one row left for it. That is much faster than one box at a time. The same goes for three boxes stacked in a column.
- Don't start with notes. Keep going without notes until hidden singles run out. Writing candidates in every cell takes time.
- Look around the digit you just placed. After placing a digit, check its row, column and box straight away for the next cell to decide. The next move is often right next to a new clue.
- On a computer, use the keyboard. Arrow keys move, 1–9 write a digit, Shift+digit writes a note, Space turns notes on and off, Backspace erases, Ctrl+Z undoes, and H asks for a hint.
- The exception: digits with only two places. If a digit can only go in two cells of a box, note it small in just those two cells. It is faster than filling every cell, and it makes pairs and pointing lines easier to notice.
10How hard each level is
- Easy: solved with the basic ways alone (hidden singles and naked singles). For first-timers and children.
- Medium: uses notes, and now and then needs pointing or claiming.
- Hard: needs pairs, hidden pairs and the like.
- Oni: needs the X-Wing and the XY-Wing.
- Master: beyond Oni. Needs techniques one step further, such as the Skyscraper and the XYZ-Wing.
Every sudoku in the Puzzle Lounge has been checked to be solvable in the same steps a person would take. The levels are set by the techniques a puzzle needs.
Typical times to finish
These times come from finished solves in the Puzzle Lounge (as of November 2026). "Median" is the time half of the solves beat. "Top quarter" is the time the fastest quarter of solves beat.
| Level | Median | Top quarter | Solves |
|---|---|---|---|
| Easy | about 5 min | about 3 min | 112 |
| Medium | about 15 min | about 7 min | 68 |
| Hard | about 21 min | about 11 min | 31 |
Solves that used hints are included. Oni and Master have too few solves yet, so they are left out.
Play sudoku free →11Print and solve
If you like to solve with pen and paper, try the printable sudoku. 2,000 puzzles from Easy to Oni, free, printed large on A4. The answer is on the second page. You can also print blank grids. They are good for a daily puzzle, or to solve together with family and older relatives.
See the printable sudoku →12Questions
Can I solve one on my first try?
Yes. Easy puzzles can be solved to the end with just two ways of looking: find where a digit can go, and narrow down what a cell can hold. There is no arithmetic.
Where can I see the answer?
When you solve on screen, press Hint. Hints go a step at a time: first where to look, and last the digit for the cell. For a printed puzzle, the answer is on the second page.
Do I need to guess or use trial and error?
No. Every sudoku in the Puzzle Lounge has been checked to be solvable by logic alone, without guessing (trying a digit to see what happens) or proof by contradiction.
Is it free? Do I need an app?
It plays free in your browser, with no app to install and no sign-up. The printable puzzles are all free too.
Can I solve with friends?
Yes. In Solve together, send an invite link and you solve the same board together. You see the cell each friend has selected in their colour. Your notes are your own.