Sudoku by the Numbers

How Hard Are Sudoku Puzzles?

A puzzle's level is the hardest technique it needs. We solve it with the Easy techniques only, then add the Medium ones, and so on. The first level that finishes the puzzle is its level, on the same five-level scale as the Learning Hub.

Hard is the most common level: 43.7% of all puzzles. Beyond logic means none of the 28 techniques our solver knows can finish the puzzle; it takes trial and error. The Solver grades any puzzle you enter the same way.

Used Is Not the Same as Needed

A solver tries its techniques in a fixed order, so it often uses one where another would also work. To find what a puzzle really needs, we took each technique away and solved again with every other technique of the same level or easier. If the puzzle can no longer be finished, it needs that technique.

The gap is large. Our solver used a Naked Pair in 64,260 puzzles, but only 197 need one. A Hidden Pair: used in 29,231, needed in 519.

We also asked a harder question: can the puzzle be finished without the technique if all 27 others are allowed, at any level? When it cannot, the technique can't be replaced. An XY-Wing is needed in 2,113 puzzles, yet a harder technique can always do its job instead. An XY-Chain can't be replaced in all 5,512 puzzles that need one.

Every Technique, Counted

How many of our puzzles need each technique, and what share of all of them that is. Each name links to its lesson.

Never needed: Remote Pairs, XYZ-Wing and WXYZ-Wing. Every puzzle where the solver used one could be finished another way at the same level. Naked Singles are needed in every Easy puzzle, since they are the only Easy technique.

Do More Clues Make a Puzzle Easier?

Only up to a point. The average number of clues at each level:

Hard, Extreme and Diabolical puzzles all average about 25 clues, and the puzzles beyond logic average 27.5, more than the Hard ones. Past Medium, the number of clues tells you almost nothing about how hard a puzzle is.

How We Counted

• The puzzles: every Classic puzzle on Sudoku Challenge (160,000+), counted in October 2026.
• The techniques: the 28 our solver knows, each with a lesson in the Learning Hub, on its five-level scale.
• Level: the first level whose techniques finish the puzzle.
• Needed: without the technique, using every other one of the puzzle's level or easier, the puzzle cannot be finished.
• Can't be replaced: without the technique, even with all 27 others, the puzzle cannot be finished.
• Beyond logic: none of the 28 techniques finishes the puzzle. It needs trial and error, or a technique our solver does not know.
• These are counts for our puzzles. A collection made another way will give other numbers.

Cite This Page

You are welcome to use these figures. Please link to this page as the source:

Sudoku Challenge, “Sudoku by the Numbers”, https://sudokuchallenge.com/sudoku-by-the-numbers, October 2026.