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Difficulty levels by solving method
A Sudoku's level is set by the solving methods it needs, and by how often it needs them. Up to Easy, the levels use only the basic methods and differ in how many numbers are given at the start. From Moderate on, each level needs harder methods, or the same methods more often. Each book teaches the methods of its levels, with worked examples.
Which range suits you?
You do not need to know the method names to choose. Each book covers one range:
- Super Easy to Easy: for beginners and relaxed solving. Super Easy · Very Easy · Easy
- Easy to Medium: for those who want a bit more challenge. Easy · Moderate · Medium
- Medium to Hard: for experienced solvers. Medium · Challenging · Hard
The levels in detail
“+” means: in addition to the methods of the easier levels above.
- Super EasyAt least 41 numbers givenNaked singleHidden single
- Very Easy34 to 40 numbers givenNaked singleHidden single
- EasyAt most 33 numbers givenNaked singleHidden single
- ModeratePointing lines or naked pairs once, with a simple result+ Pointing lines+ Naked pairs
- MediumPointing lines or naked pairs up to 3 times+ Pointing lines+ Naked pairs
- ChallengingPointing lines or naked pairs 4 or more times, or a hidden pair or naked triple once or twice+ Hidden pairs+ Naked triples
- HardHidden pairs or naked triples 3 or more times, or a hidden triple or X-Wing+ Hidden triples+ X-Wing
The methods in one line each
- Naked single
- Only one number fits the cell. Also called single candidate.
- Hidden single
- A number fits in only one cell of a row, column or box. Also called single position.
- Pointing lines
- In a box, a number can go only in one row or column, so it cannot go in that row or column outside the box. Or the other way round: in a row or column, a number can go only in one box, so it cannot go in the rest of that box. Also called pointing pairs or box-line reduction.
- Naked pair
- Two cells of a row, column or box can hold only the same two numbers. Those numbers cannot go in the other cells there.
- Hidden pair
- Two numbers can go only in the same two cells of a row, column or box. No other number can go in those two cells.
- Naked triple
- Three cells of a row, column or box hold only three numbers between them. Those numbers cannot go in the other cells there.
- Hidden triple
- Three numbers can go only in the same three cells of a row, column or box. No other number can go in those cells.
- X-Wing
- In two rows, a number can go only in the same two columns. So it cannot go in the other cells of those two columns (and the same with rows and columns swapped).
Harder methods exist too, such as Swordfish and Y-Wing. Books and apps that use them call their levels Very Hard, Expert or Extreme. Our books go up to X-Wing: every Sudoku in them can be solved with the methods above.
Pencil marks are not a method of their own: they are the small numbers you write in a cell for every number that can still go there. The harder methods need them; easier Moderate and Medium Sudokus can sometimes be solved in your head.