Extreme sudoku printable

Graded by the hardest step, on every sheet

Most extreme sudoku are labelled by how few clues they have. That says little: of the original 24 boards on this page, sorted by clue count, nine can be finished with singles alone. So every newer board here is solved by a program that works the way a person does, simplest technique first, and the hardest technique it had to use is printed in the title and under the board. A sheet marked X-wing cannot be finished without an X-wing, and that is checked twice: the simpler techniques are run on their own and have to get stuck.

The ladder the grades come from

From the bottom: singles, locked candidates, pairs, triples and quads, X-wing, swordfish, XY-wing, XYZ-wing, jellyfish, X-chain, XY-chain. The X-chain rung covers skyscrapers, two string kites and longer chains on a single digit. A grade means everything below it stalls and nothing above it is needed. A board that asks for more than the ladder holds is left out of the graded groups.

What is the difference between hard, extreme and evil sudoku?

On this site, hard means about 26 clues, and most of those boards fall to singles and candidate notes. Extreme is a board that stalls on singles and needs a named pattern such as a triple, an X-wing or a swordfish. Evil is the top group here: the hardest step is a wing or a chain.

How to read a card

The title gives the grade and the clue count. The description adds how many digits fall to singles before the first stall, and how many squares are still open when the hardest step arrives. A board that stalls after 5 digits with 50 squares open is a long sit. One that gives up 33 digits first leaves a short, sharp finish.

Answer pages that show the move

Every graded PDF ends with the full solution, the digits you had to find in pink, and one line naming the hardest step with its cells: "X-wing on 2: rows 1 and 5, columns 1 and 9". Six sheets go further and add a middle page with the board as it stands just before that step, candidates pencilled in, pattern cells tinted and the removed candidates struck out.

Clue counts on this page

Seventeen is the proven minimum for a sudoku with one solution, but a board that empty is a rare find and no generator turns one out to order. Of the first 100,000 boards dug for this page, none went below 20 clues and five reached it. Those five are in the low clue group, next to three boards at 21. The rest run from 22 to 27.

Printing

Each board takes one A4 page with 20 mm squares, enough room for candidate notes; the large print boards use 21.1 mm squares. Print at 100 percent or actual size, never fit to page, and avoid draft mode so the thin grid lines survive. A fine pencil and a clean eraser help.

If two or three boards in a row refuse to open, step back to hard sudoku at around 26 clues or to medium sudoku with 33. Every level is listed on printable sudoku, and large print sudoku is the page for when square size matters more than difficulty. For a different kind of hard, killer sudoku swaps most or all of the given digits for cages with totals.