What Sudoku difficulty levels actually mean

Almost every Sudoku app labels its puzzles Easy, Medium, Hard and Expert, and almost none of them explains what the labels measure. The common guess — that difficulty is the count of numbers you start with — is wrong, and believing it makes harder puzzles feel arbitrary rather than learnable.

The starting numbers barely matter

The digits printed in the grid before you begin are called givens or clues. It is tempting to treat them as a difficulty dial: more clues, easier puzzle.

They are a weak signal at best. Two grids with the same number of clues can be worlds apart, because what matters is not how many clues there are but where they are. Clues clustered into a few boxes leave large open regions that resist every simple deduction. The same clues spread evenly can make the whole grid fall apart in a few minutes.

You can prove this to yourself on a single puzzle: erase one given from an easy grid and the puzzle often stays easy. Erase a different one and it can become genuinely hard. The count changed by one either way.

What actually sets the level

A well-graded puzzle is rated by the hardest step it forces. A solver — human or software — walks the grid using the simplest available move at each point, and only reaches for a more advanced one when nothing simpler works. The most advanced move the puzzle ever requires is its difficulty.

Roughly, the ladder goes:

1. Singles. A cell where only one digit fits, or a digit that fits only one cell in its row, column or box. A puzzle solvable entirely with these is an Easy puzzle, no matter how few clues it started with.
2. Candidate eliminations inside one unit. Two cells that can only hold the same two digits lock those digits away from the rest of the row. Nothing is placed; possibilities are removed. This is where Medium usually lives.
3. Patterns that span several units. A digit confined to the same two columns in two different rows rules itself out everywhere else in those columns. Hard puzzles need a few of these.
4. Chains. Following a chain of "if this cell is a 5, then that one isn't" until a contradiction appears. Expert territory.

That is the whole scale. Each rung is a specific, nameable move — and every one of them can be learned. Our technique guides work through them in that order, each with a worked example and practice puzzles that were checked by a solver.

Why "Expert" should never mean "guess"

There is one more property a graded puzzle must have, and it is the one that separates a serious app from a puzzle generator someone wrote in a weekend: a proper Sudoku has exactly one solution, reachable by logic alone.

If a puzzle ever requires you to pick a digit at random and see whether it works out, it is not a hard puzzle. It is a broken one. Difficulty should come from the deductions getting subtler, never from information being missing.

This is checkable, not a matter of taste. Every puzzle we publish on the site — including every daily challenge — is walked from start to finish by the same hint engine the app uses, and rejected if the engine ever has to fall back on reading the answer instead of deducing it.

How to use the labels

Once you know the scale measures technique depth, the labels become a study plan instead of a difficulty warning:

• Stuck on Easy? You are missing singles somewhere. Slow down and scan digit by digit rather than cell by cell.
• Comfortable on Medium, stuck on Hard? You almost certainly need to start writing candidates down. Hard puzzles turn on eliminations, and eliminations are invisible if you are holding everything in your head.
• Stuck at one specific point in an Expert grid? That is the useful kind of stuck. There is a named technique for whatever is blocking you, and learning it once fixes every future puzzle that uses it.

If you are starting from the beginning, the three rules and how to apply them is the place to begin. If you want a graded puzzle a day with a full worked solution published the following morning, that is what the daily challenge is for.