Sudoku Difficulty Levels

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Published May 5, 2026 · Updated October 20, 2026

A difficulty label is a promise about how hard the reasoning will get, and every site keeps that promise its own way. This page covers how labels are usually set, then exactly how ours are: how our generator builds Easy to Expert, where Evil and Extreme come from, and what each level asks of you, counted on the puzzles we deal.

What do sudoku difficulty levels mean?

A level names the hardest kind of reasoning a puzzle forces on you. Rating programs find it by solving the puzzle the way a person would, simplest technique first, and looking at what they had to use. They differ in how they turn that into a grade:

• Sudoku Explainer rates a puzzle by the most advanced technique it needs, on a scale where the last value in a box scores 1.0 and an X-Wing 3.2, as Sudoku Exchange’s puzzle bank explains.
• HoDoKu adds up a score for every step, so a puzzle with many hard steps grades above one with a single hard step. Its levels run Easy, Medium, Hard, Unfair and Extreme, and its manual warns that because the scoring is configurable it “can’t therefore provide an absolute measure of difficulty”.
• SudokuWiki files its solver’s strategies under Basic, Tough, Diabolical and Extreme.

So a label means something only against the list of techniques behind it, and the lists differ. A Hard puzzle from one site can need an X-Wing; a Hard one from ours never does.

How are our difficulty levels built?

Easy, Medium, Hard and Expert are made fresh for every game by the generator behind our classic sudoku. It fills a complete grid, then takes digits away one at a time in random order, and keeps a removal only if the techniques allowed at that level can still solve what is left. It stops at the level’s target. If one pass can’t get that far, it starts again in a new order, up to six times, and keeps the attempt with the fewest digits. Because those techniques must finish every board, each one is also proved to have exactly one answer.

Easy to Expert: 200 boards per level from the generator. Expert aims at 22 and got there on 29 boards; 118 stopped at 23, 52 at 24 and one at 25. Evil and Extreme: every puzzle in each bank. Measured October 2026.

Evil and Extreme are not dug at all. Evil deals from 5,000 puzzles taken from a public collection of random minimal puzzles; Extreme takes 4,980 of its 5,000 from the list of the hardest known puzzles kept on the Enjoy Sudoku forum. Each page tells its bank’s story in full. We counted every one of the 10,000: each has exactly one answer. Our 17-clue sudoku page is a third bank, 49,158 puzzles with the fewest givens a sudoku can have.

The levels have been built this way since 10 October 2026. Before that the generator aimed only at a number of givens, and when we measured it then, 3 Medium boards in 40, 12 Hard and 11 Expert needed more than singles, locked candidates, pairs, triples and X-Wings.

How hard is each of our levels?

We walked every puzzle three ways, always taking the simplest move: with naked singles only, with naked and hidden singles, and with all eighteen techniques of our Sudoku Helper.

The same boards and banks as the table above. “All singles” means naked and hidden singles together; the helper tries its eighteen techniques in a fixed order, simplest first. Measured October 2026.

Read down the columns and the levels separate cleanly. Medium asks for nothing Easy doesn’t; it just hides more of it. Naked singles alone finish 192 Easy boards but only 94 Medium ones, and the rest need a hidden single somewhere. Hard needs locked candidates on 23 boards in 200, each time a pointing pair or its mirror image, box/line reduction; Expert needs them or a naked pair on 68. The rest of the helper’s list, from hidden pairs to simple colouring, is needed only from Evil up, and our sudoku techniques page counts how often each one is.

Does fewer clues mean a harder sudoku?

No, and our banks show it plainly. We took every tenth line of the 17-clue bank, 4,916 puzzles in all: singles alone finish 2,165 of them, 44%, and the helper’s eighteen finish all but 123. Not one Evil puzzle falls to singles, though Evil starts from a median of 26 givens, the same as Hard, where singles finish 177 boards in 200.

The two puzzles above make the point at its sharpest: the emptier grid is the easy one. Givens decide how much there is to read at the start, not how hard the reading is. Why 17 is the floor is on the 17-clue page.

Which level should you play?

Pick by the techniques you have, not by the name:

• New to sudoku: Easy. You can finish almost every board by finding squares with one digit left, and our sudoku strategies for beginners walks a real one.
• You can find where a digit must go in a box: Medium, which asks for exactly that more often.
• You keep pencil marks: Hard, where 23 boards in 200 call for a pointing pair or a box/line reduction.
• You know naked pairs: Expert. Nothing past them is ever needed.
• You know hidden pairs, X-Wings and wings: Evil, where the helper’s eighteen finish almost three puzzles in four.
• You work forcing chains: Extreme.

Move up when a level stops making you stop. If you stall at the same kind of position again and again, put it into the Sudoku Helper: its hint names the technique, and the Sudoku Trainer drills it on real boards.

Why does a puzzle feel harder than its level?

Three common reasons. Boards within a level differ: singles alone finish 132 of our 200 Expert boards, but on the 66 that needed a pointing pair, the first one came at a median of move 15, with 44 squares still empty. Labels differ between sites, so a Hard puzzle from a newspaper or an app may need techniques ours never ask for. And a missing pencil mark makes any puzzle feel impossible; sudoku mistakes shows how one goes wrong and how to find it.

Can every sudoku be solved without guessing?

Every puzzle we deal has exactly one answer, so a chain of reasoning to it always exists. The question is how long the chain is. On Easy to Expert the generator has already proved it short: the named techniques finish the board. On Evil the helper’s eighteen finish 3,655 puzzles in 5,000; on the first 500 we went further, and with chains added every one of them finished, as our forcing chains guide shows. Extreme’s forum puzzles need chains nested inside chains, and whether that is still logic or careful guessing is a question that guide takes up.