Sudoku Generator

Difficulty in Sudoku is set by how many numbers are filled in at the start (called "givens"). Easy puzzles start with 36 to 40 givens, medium with 28 to 32, hard with 22 to 26 and expert with the absolute minimum of 17 to 21. The lower the count, the more the solver has to deduce.

An easy Sudoku can usually be solved by simple scanning - look at where a 7 already appears in the grid and work out which empty cell in each row, column or 3x3 box must hold the next 7. Medium puzzles need pencil notes (writing candidates in the corners of cells) and basic techniques like "hidden singles". Hard puzzles require pattern-spotting techniques: pointing pairs, naked triples, X-wings. Expert puzzles, with just 17 starting clues, often need chain logic or trial-and-error in a worst case. The rule that every valid Sudoku must have exactly one solution still applies at every difficulty.

Scanning, hidden singles and naked pairs will solve almost every easy and medium Sudoku and will get you through most hard ones. Scanning means looking at each digit 1 through 9 in turn and finding rows, columns or boxes where it can only fit in one cell. Hidden singles means looking inside a row, column or box and finding a cell that can only hold one specific number even though several others might seem possible.

Naked pairs is the next step up: when two cells in a row both contain the same two candidate numbers and nothing else, you can eliminate those two numbers from every other cell in that row. Switch on pencil mode in the generator (the ✎ Pencil button) to write candidates into cell corners as you work. The grid also highlights every cell that shares a row, column or box with your selected cell, plus every other cell containing the same number, which makes spotting these patterns much faster than working with paper.

Click Download PDF for a print-ready puzzle on a single A4 page. The Solution PDF gives you the answer key on a separate sheet, useful for classroom worksheets where you mark students' work or for pub quiz hosts running a Sudoku-as-tiebreaker round. Both files are watermark-free.

For schools, easy and medium puzzles work well as 5-to-10-minute filler activities for years 4 through 7. Hard and expert make sensible "if you finish early" enrichment material. For long flights, generate three or four hard puzzles before you board - solving without a phone for hints adds about 50% to typical times because the highlighting tools are not available. The grid here uses standard Sudoku notation with thick lines on the 3x3 box borders, so puzzles printed from this tool look identical to those in newspapers and puzzle books.