Sudoku Difficulty Levels Explained
Pick a Sudoku anywhere and you are asked to choose a difficulty before you have seen a single grid. The labels look official - Easy, Hard, Expert - but there is no standards body for Sudoku difficulty. Every site invents its own ladder, its own names and its own number of rungs, and none of them have to agree.
That is worth knowing before you decide a level is "too hard for you". You may simply have met a steeper ladder.
Nobody agrees on the names
Three sites, three different ladders:
- SudokuStreak - five levels: Easy, Medium, Hard, Expert, Evil.
- Web Sudoku - four levels, described on its own site as "four levels from Easy to Evil".
- Sudoku.com - six levels: Easy, Medium, Hard, Expert, Master, Extreme.
So "Expert" is the fourth rung of five in one place and the fourth of six in another, and the hardest tier is called Evil here and on Web Sudoku but Extreme on Sudoku.com. We deliberately don't quote anyone else's clue counts on this page - we have not verified them, and an unverified number is worse than no number.
The one thing that is comparable across sites is the count of clues you start with. Compare that, not the adjective.
What each level means here
On SudokuStreak the ladder is set by how much of the grid you are given, out of 81 cells:
Easy - 36 givens
A little under half the grid is already filled. There is always an obvious next move somewhere, so you can finish an Easy puzzle knowing only how to scan a row, column or box for the one cell a digit can go in. No pencil marks needed. This is the level to learn on, and the level to come back to when you want a puzzle that does not fight you.
Medium - 30 givens
Six fewer clues than Easy, which sounds like nothing and is not. The board stops handing you free moves: you clear the obvious cells quickly and then hit the first honest pause, where nothing jumps out and you have to look properly. This is usually where solvers start writing candidates down.
Hard - 26 givens
The level where guessing stops paying off. Scanning gets you started and then leaves you stranded, and the grid will not move again until you work on candidates rather than on digits - naked and hidden pairs, and pointing pairs. If you have never used a pencil-mark technique, Hard is where you will need your first one.
Expert - 22 givens
Beginner tools dry up almost entirely. Where a Hard grid bends to a naked pair, an Expert grid often needs a genuine advanced pattern before anything moves at all - the X-Wing, the XY-Wing, or a short forcing chain. It is the level most solvers plateau on, and the one worth staying at until the advanced patterns come without hunting.
Evil - 18 givens
The hardest we make, and one single clue above the proven mathematical minimum of 17. There is barely any redundancy left in the grid, so the openings dry up within a handful of placements and you work almost entirely on candidates.
Play Evil Sudoku - and What Is Evil Sudoku? goes into that level on its own, including where the name came from.
Why clue count is not the whole story
Fewer clues generally means a harder puzzle, but the link is not exact. A well-constructed 22-clue grid can be nastier than a plain 18-clue one: the count sets the floor of the difficulty, and the arrangement of those clues decides the rest. Two puzzles with identical clue counts can need completely different techniques.
That is also why 17 is famous. In 2012 a team at University College Dublin proved by exhaustive computer search that no valid 16-clue Sudoku exists - the full story is here. Seventeen is the floor for a puzzle with exactly one solution.
Which level should you play?
The useful test is not "can I finish it" but "does it teach me anything". A level you clear without pausing is practice, not progress; a level where you stall for twenty minutes and then spot the pattern is where you actually improve.
A reasonable route: stay on Easy until scanning is automatic, move to Hard when you are comfortable writing candidates, and treat Expert as the long plateau where the advanced patterns get learned properly. Evil is worth it once an X-Wing is something you notice rather than something you go looking for.
If you want the map rather than the ladder, Sudoku Techniques by Difficulty lists every technique in the School in the order they become useful.
Does a harder level mean guessing?
No, at no level. Every puzzle here has exactly one solution and that solution is reachable by pure deduction. What changes as you climb is which patterns you need to see it - not whether logic is enough. If a site's hardest puzzles genuinely force you to guess, they are not hard, they are broken.