25–29 clues · typical solve 20–40 minutes
Printable hard sudoku puzzles: free PDF, answers included
Sparse grids that open up once you reason about where each digit cannot go.
Set a hard run
difficulty is already set to hard; adjust the rest
1–60 · the solver checks each puzzle for a single solution before adding it
This sample switches to your own puzzles when the run finishes.
What a hard sudoku asks of you
A hard sudoku gives you 25 to 29 clues. Scanning fills a handful of cells, and after that you make no progress until you fill in candidates and work with the relationships between them. Pointing pairs, box-line reduction and hidden pairs do the work here. On a medium puzzle they feel like overkill; on this one you need them.
Hard puzzles use the same logic as easier ones, with less redundancy. An easy grid usually offers three routes to the next cell, so you find one without trying. A hard grid often offers one deduction on the whole board, and you find it by searching the board in order. This level trains that systematic search.
Expect twenty to forty minutes, expect to put the grid down and come back, and expect the odd mistake. A careless entry on a hard grid can sit unnoticed for twenty moves. Print the answer key so you can check a finished grid, and print one or two per page for room to write.
Printable hard sudoku: questions
How many clues does a hard sudoku have?
Between 25 and 29. Each puzzle prints its clue count under the grid, so you can see how sparse the one in front of you is.
What techniques do I need for hard sudoku?
You need candidate marking, and on top of that naked and hidden pairs, pointing pairs and box-line reduction. Our solving techniques guide works through each with examples.
Do hard puzzles ever require guessing?
No. Each puzzle here has one solution and yields to logic. If you are guessing on a hard grid, you have probably missed a deduction, and a wrong guess on a sparse grid can take twenty minutes to unpick.
Should I print hard puzzles one per page?
Print one or two per page. Hard puzzles need candidate marks in nearly every empty cell, and a six-per-page grid leaves too little room to write them legibly.
Try another level
Each level uses the same generator and the same uniqueness check, and only the clue count changes. Try the next level up or down if this one is too easy or too hard.
- Easy printable sudoku38–45 cluesPlenty of clues, and a solving path you can find by scanning alone.typical solve: 5–10 minutes
- Medium printable sudoku30–37 cluesThe everyday sudoku, at the level a newspaper prints midweek.typical solve: 10–20 minutes
- Expert printable sudoku20–24 cluesAbout a quarter of the grid filled in, and one solution to reach.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.