Variations
What prints with the starting settings
| Paper | US Letter — 215.9 × 279.4 mm (8.5 × 11 in) |
|---|---|
| Difficulty | Hard — 27 clues, unique solution |
| Puzzles per page | 4 |
| Margins | 1/2″ |
| Line weight | 0.18 mm (bold 0.35 mm) |
| Print setting | Scale 100% / Actual size |
For experienced solvers
With about a third of the squares given, scanning is slow, and in many hard puzzles it stops altogether. When you reach a point where no square has an obvious answer, the way forward is to write the possible digits (candidates) in each empty square and look for patterns among them.
Techniques that help
- Naked pairs: two squares in a unit that share the same two candidates remove those digits from the rest of the unit.
- Pointing: if a digit’s candidates in a box all sit in one row, that digit can be removed from the rest of the row.
- Hidden singles: a digit that has only one possible square in a row, column or box goes there, even if the square has other candidates.
- X-wing: a digit restricted to the same two columns in two rows can be removed from those columns elsewhere.
The how to solve sudoku guide walks through the basics. For a warm-up, try the easy puzzles first.
Fresh puzzles every time
Change the puzzle book number for a new set. The same number always prints the same puzzles, so a club or class can all work on identical grids.
Printing
Print at 100% / Actual size on plain white paper. Two or one per page is best for hard grids because of the pencil marks.
More sudoku sheets
Frequently asked questions
How many clues does a hard puzzle have?
Between 26 and 28. The generator aims for 27, removing clues in symmetrical pairs only while the puzzle keeps a unique solution, and starts again if a grid stalls above 28.
Do I need to guess?
No. A built-in solver grades every hard puzzle: each one needs more than simple scanning, but none needs anything beyond the X-wing, so all of them can be finished by logic. In a test of 200 hard puzzles, about 4 in 10 needed pencil marks and techniques such as pairs or pointing.
Why print fewer per page?
Pencil marks need space. With two per page each square is about 1.3 cm, large enough for small candidate digits in the corners.
Is there an answer key?
Yes. An answer page follows each page of puzzles, with the original clues in bold.
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