There is no official grading standard for Sudoku puzzles nor standardization of labels for level of difficulty. It is up to the Sudoku creator to choose the appropriate label for the difficulty level. It is a subjective decision and can vary by skill level and experience. Puzzles that are easy for one person can be hard for another.
Which do you think is more difficult, a puzzle labeled advanced, evil, black belt, devilish, extreme, fiendish, nasty or expert?
Are puzzles labeled easy, beginner, novice, simple, basic or "for dummies" the same?
Puzzle Books Plus helps you feel confident selecting a book of Sudoku puzzles at the level you want, because we use a consistent standard for naming and grading Sudoku levels. The level is determined by the logic techniques needed to solve the Sudoku.
See How to Solve Sudoku Puzzles for explanations and examples of the logic techniques used to categorize our Sudoku levels.
Puzzle Books Plus Difficulty Levels:
Easy Sudoku can be solved using only techniques to identify Naked Singles and Hidden Singles. This level also includes "Easier" puzzles with only Naked Singles and "Easiest" puzzles with only Naked Singles plus extra starting numbers.
Medium Sudoku can be solved using the techniques for "Easy" Sudoku - plus Block-Line Interaction, Block-Block Interaction, Naked Pairs and Hidden Pairs.
Hard Sudoku can be solved using the techniques for "Medium" Sudoku - plus X-wing, XY-wing, XYZ-wing, XY Chain, Forcing Chains, Coloring, Naked Triples and Hidden Triples.
Very Difficult Sudoku can be solved using the techniques for "Hard" Sudoku, but will require the use of multiple “hard” solving strategies in a single Sudoku.
Currently we do not publish Sudoku books that require more advanced solving techniques, such as Swordfish, but plan to add more advanced Sudoku books in the future.
All our Sudoku puzzles have a unique solution which can be found using these logic techniques. If you do not have experience with some of these solving methods, you may get stuck and feel as if you have to resort to trial and error. However, the puzzles in all our published Sudoku books can be solved without using trial and error.