25–29 clues · typical solve 20–40 minutes
Printable hard sudoku puzzles — free PDF, answers included
Sparse grids that will not open up until you start reasoning about where digits cannot go.
Set a hard run
difficulty is already set to hard — adjust the rest
1–60 · each puzzle is solver-checked for a single solution before it goes in
This is a live sample puzzle — it updates to your own puzzles once the run finishes.
What a hard sudoku asks of you
A hard sudoku hands you 25 to 29 clues and expects you to do the rest. Scanning gets you a handful of cells; after that the grid goes quiet, and it stays quiet until you fill in candidates and start working with the relationships between them. Pointing pairs, box-line reduction and hidden pairs all earn their keep here — techniques that feel like overkill on a medium puzzle and feel like the only way forward on this one.
The difference is not that hard puzzles have more difficult logic in them. It is that they have less redundancy. On an easy grid there are usually three different routes to the next cell, so you find one without trying. On a hard grid there is often exactly one deduction available on the whole board, and finding it means looking systematically instead of hopefully. That is the skill this level trains.
Expect twenty to forty minutes, expect to put it down and come back, and expect to be wrong occasionally — a hard grid punishes a careless entry twenty moves later, which is when you discover it. Print with the answer key so you can check your finished grid rather than wondering, and print one or two per page: you will want the room to write.
Printable hard sudoku — questions
How many clues does a hard sudoku have?
Between 25 and 29. Each puzzle prints its own clue count under the grid, so you can see exactly how sparse the one in front of you is.
What techniques do I need for hard sudoku?
Candidate marking is essential, and beyond that you will lean on naked and hidden pairs, pointing pairs and box-line reduction. Our solving techniques guide walks through each of them with worked examples.
Do hard puzzles ever require guessing?
No. Every puzzle here has exactly one solution and every one can be solved by logic. Guessing on a hard grid is usually a sign that a deduction has been missed, and it is a bad trade — a wrong guess on a sparse grid can take twenty minutes to unpick.
Should I print hard puzzles one per page?
One or two per page is the sensible choice. Hard puzzles need candidate marks in nearly every empty cell, and a six-per-page grid does not leave enough room to write them legibly.
Try another level
Too easy or too hard? Every level uses the same generator and the same uniqueness check — only the clue count changes.
- Printable sudoku — easy38–45 cluesGenerous clue counts, no guessing, and a solving path that opens up the moment you start scanning.typical solve: 5–10 minutes
- Printable sudoku — medium30–37 cluesThe everyday sudoku — the level a newspaper prints on a Wednesday.typical solve: 10–20 minutes
- Printable sudoku — expert20–24 cluesStripped to the bone — around a quarter of the grid filled in, and a single solution waiting at the end of it.typical solve: 40 minutes to over an hour
Or head back to the free printable sudoku generator for a mixed run, or take a set of printable sudoku with answers.