Sudoku Maker (4×4 to 16×16, with Answer Key)

What it is for

This tool prints sudokus for a classroom, a puzzle club or your own coffee break. You pick the grid size, the difficulty and how many puzzles go on a page; you get a true-size PDF with the puzzles first and the answer key after them, plus SVG and PNG of the first page.

Sizes run from 4 × 4 (boxes of 2 × 2, good for young children) through 6 × 6, 8 × 8 and the classic 9 × 9 to 12 × 12 and 16 × 16, which use the letters A–G after 9. Every puzzle has exactly one solution: a clue is only removed when a solver proves that no second solution appears.

Worked example

The default run makes four medium 9 × 9 sudokus with the seed sudoku-1. The summary reads "4 sudokus of 9 × 9 (medium) on 2 pages, each with exactly one solution": page 1 holds the four puzzles, page 2 the answer key. They keep 27 or 28 clues each, and the table lists every grid row by row with a dot for each empty cell.

For children, six easy 6 × 6 sudokus with six per page give 16 clues each — easy puzzles always keep at least 45 % of the cells. A hard 12 × 12 puzzle (seed big-1) has 54 clues. Even a 16 × 16 easy grid (seed guide-16) comes out in well under a second with 116 clues.

Change the seed and you get a new set; keep it and the same sheet comes back, in the tool and in Printshop.

How to read the result

• Difficulty is measured, not guessed. A logic solver tries human techniques from simple to hard: naked and hidden singles (easy), locked candidates (medium), naked and hidden pairs, naked triples and X-wing (hard). The hardest one it needed is the grade. Expert means none of these finish the puzzle — it needs chains or trial and error.
• requested shows what you asked for. If a puzzle could not be dug to that level, the printed grade is the real one and a warning says so.
• clues is the number of given cells; puzzle and solution are the grids as text.
• pages, puzzlePages and answerPages count the PDF pages; the files are the PDF, the first page as SVG and a PNG preview.

Tips and common mistakes

• Print at 100 % ("actual size"); the page layout already fits A4 or Letter with margins.
• Turn off Answer-key pages when you hand the PDF to the people who will solve it.
• Symmetric clues gives the classic look (the pattern of givens turns into itself by 180°); switching it off sometimes allows fewer clues.
• For beginners, start with 4 × 4 or 6 × 6 easy: those only need singles.
• 16 × 16 sudokus have a time budget. If it runs out, the puzzle keeps a few extra clues and a warning tells you; it still has one solution.

FAQ

Why is my "hard" puzzle graded medium?

Random digging rarely needs the hard techniques. The tool tries several digging orders and keeps the closest match; if none reaches the level, it prints the honest grade.

Can I solve the puzzles on screen?

Yes. Open the result in Printshop and press Play on screen…: type into the cells, check your entries or show the solution.

Are killer or jigsaw sudokus possible?

Not yet — only classic sudokus with rectangular boxes.

How do I make different sheets for a group?

Use a different seed per sheet, for example class-1, class-2.