The basics
Sudoku difficulty levels explained
A level label means little unless you know what it measures. Here is how our five levels are defined and how to choose.
Difficulty depends on the hardest technique a puzzle needs, not on how many digits are given. Easy needs only singles, Medium adds pairs and pointing pairs, Hard needs triples, Expert needs X-Wing or Swordfish, and Extreme needs XY-Wing or coloring.
Why clue count is a poor measure
Many sites rate difficulty by how many digits are given. That is unreliable: a puzzle with 24 clues can be easy, and one with 30 clues can be brutal. What really decides is which solving technique you must use at the hardest moment.
Our five levels
- Easy: naked singles and hidden singles only.
- Medium: adds naked pairs, hidden pairs, pointing pairs and box-line reduction.
- Hard: needs naked triples or hidden triples.
- Expert: needs X-Wing or Swordfish.
- Extreme: needs XY-Wing or simple coloring.
A puzzle is placed in the level of the hardest technique it needs, found by solving with the easiest available technique first. Harder techniques are used only when nothing easier makes progress.
How to choose your level
- If you finish a level in under about ten minutes without hints, move up.
- If you are stuck for more than twenty minutes, check the technique list for the level below.
- It is normal to play two levels: a comfortable one for relaxing and a harder one for learning.
Other sites use different names
Labels like Evil, Diabolical, Master or Fiendish are not standardized. Our Extreme level is similar to what many sites call evil. Always judge by the techniques required, not by the name.
Frequently asked questions
What makes a Sudoku hard?
The techniques you need to find the next digit. Puzzles that require chains or fish patterns are harder than ones that only need singles.
Does fewer clues mean harder?
Not necessarily. Many easy puzzles have few clues, and many hard ones have more.
What is the hardest Sudoku level?
On this site, Extreme. Some other sites go further with levels that require chains longer than XY-Wing.