Step 1: Identify the givens
Understand the starting board before you place anything.
5
3
7
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
Look here firstEach Sudoku puzzle starts with its own set of given numbers already on the board. You use them to solve the puzzle, but you cannot change them.A given number appears as a fixed clue on the board.
The empty squares are yours to fill. Every move you make has to work with the givens.
Step 2: Finish an easy row
Start with a row that is missing only one number.
5
3
6
7
8
9
1
2
6
1
9
5
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
Look here firstLook at the top row. It already has 1, 2, 3, 5, 6, 7, 8, and 9.
The only missing number is 4, so the empty square in that row must be 4.
Step 3: Check a column
Use the same missing-number idea vertically.
5
3
7
1
6
1
9
5
4
9
8
6
8
6
2
3
4
8
3
1
7
2
5
6
6
2
8
4
1
9
3
5
8
7
Look here firstLook down the eighth column. It already has 1, 2, 3, 4, 5, 6, 7, and 8.
The only missing number is 9, so the empty square in that column must be 9.
Step 4: Use the 3x3 box
Cross-check rows and columns to place a number in the box.
5
3
4
7
6
2
1
9
5
1
9
8
6
8
6
3
4
8
3
1
7
2
6
6
2
8
4
1
9
5
8
7
9
Look here firstLook at the top-left 3x3 box. It has every number except 7.
Because that box has only one empty square, the missing 7 goes there.
Step 5: Pencil Mode hints
When the easy fills slow down, use notes before committing.
5
3
1
2
4
6
7
6
1
9
5
9
8
6
8
6
3
4
8
2
5
7
9
3
1
7
2
6
6
2
8
4
1
9
5
8
7
Look here firstLook at the small numbers in the center square. They are pencil marks, not final answers.
Pencil marks help you remember what might fit while you keep solving.
Step 6: Clean up candidates
Some moves do not fill a square right away. They remove notes that cannot be correct.
5
5
7
1
5
8
9
3
5
6
7
2
9
4
8
1
9
8
3
4
2
6
7
8
9
6
4
6
8
3
1
7
3
2
6
6
4
9
8
5
2
2
4
8
7
6
Look here firstFocus on the number 5. Every possible 5 in the top-left box is on the top row.
That means the top row’s 5 must be inside that box. The other 5s in the top row, outside the box, can be removed. The board may not gain a final answer yet, but it becomes easier to solve.
5 pencil marks to keep5 pencil marks to remove
Step 7: Repeat the solving loop
Most of the middle of a Sudoku puzzle is repetition: place sure numbers, update notes, remove impossible candidates, and look again at rows, columns, and boxes.
Step 8: Finish the final square
Near the end, the last empty squares usually become forced.
5
3
4
6
7
8
9
1
2
6
7
2
1
9
5
3
4
8
1
9
8
3
4
2
5
6
7
8
5
9
7
6
1
4
2
3
4
2
6
8
5
3
7
9
1
7
1
3
9
2
4
8
5
6
9
6
1
5
3
7
2
8
4
2
8
7
4
1
9
6
3
5
3
4
5
2
8
6
1
7
Look here firstLook at the last empty square. Its row, column, and 3x3 box leave only one possible number: 9.
When every remaining check points to one answer, place it and complete the puzzle.
Want deeper strategy examples? Open the Sudoku Techniques guide.