Sudoku guide

Sudoku is not a guessing game. Every cell is decided for a reason. This guide explains the ways to find those reasons, the techniques, one at a time and easiest first. Every example comes from a real Everydoku board, and the link under each picture opens that board so you can try it yourself.

Techniques, easiest first

Read them in order if you can. Each technique builds on the ones before it.

• 1. Naked singleA cell with only one possible digit. Where every solve starts.
• 2. Hidden singleA digit with only one possible cell in a row, column or box. Trains your eye to scan.
• 3. Pencil marksHow to note candidates when you are stuck. Every later technique shows up in your notes.
• 4. Locked candidatesWhen a box's candidates line up in one row or column, clear the rest of that line.
• 5. Naked pairTwo cells sharing the same two digits keep those digits out of the rest of the line.
• 6. Hidden pairTwo digits confined to the same two cells: clear the other candidates there.
• 7. X-WingThe first advanced pattern: a rectangle of two rows and two columns.

Guides by board size

• 4×4 and 6×6 sudokuSmall boards for beginners and kids. Getting the rule into your fingers.
• 12×12 and 16×16 sudokuBig boards with the letters A to G. How to finish an hour-long board.
• Printable sudokuBoards to print by size and difficulty, with answers.

Which techniques each difficulty needs

Every Everydoku board was graded by a program that solves it the way a person would. The table shows the techniques you need at least to finish each difficulty. Each level also uses everything from the levels before it.

There are 5,000 boards for every size and difficulty (1,000 boards for 4×4). Every board has exactly one solution, so logic alone always gets you to the end.

How to read this guide

• In the board pictures, light blue marks the row, column or box being looked at, and darker blue marks the cell being solved.
• Hatched cells are lines that block other cells, and orange cells hold the digits that create those lines.
• Small digits are candidates (pencil marks). A blue circle marks the candidates that form the pattern, and red marks candidates that can be removed.
• Rows count from the top and columns from the left. Boxes are numbered from the top left, across and then down.

Want the rules first? Read How to play. Ready to solve? Play now →