Printable X Sudoku (Diagonal Sudoku) Puzzles

What is in each X Sudoku PDF?

Each of the four PDFs above is a 63-page book of 100 printable X Sudoku puzzles: the rules on the cover, two puzzles a page on pages 2 to 51, and the solutions nine to a page on pages 52 to 63. The pages are US Letter and black and white. Both diagonals are shaded light grey in every puzzle and every solution, so nothing depends on a colour printer, and there is no sign-up: each link opens the PDF itself.

X Sudoku is the same puzzle as diagonal sudoku and Sudoku X: ordinary 9×9 sudoku in which both long diagonals must also hold 1 to 9 once each. The rules in depth, and what the diagonals add, are on the X Sudoku game page, where you can also play it on screen, and the daily X Sudoku gives everyone the same board each day. This page is about the paper: what the four books hold, how to print them and how to check a finished grid. Classic sudoku and nine other kinds are on our printable sudoku page.

Does every puzzle have exactly one solution?

Yes, and we checked it three ways. The puzzles were dealt by the same generator as the online game, which starts from a finished grid and takes digits away one at a time, keeping a removal only while the puzzle still has exactly one answer under X rules. Then every one of the 400 printed puzzles was counted again by a separate solver written for the printables, sharing no code with the generator: all 400 have exactly one answer, and none had to be dealt again. Last, we read all 400 puzzles and their 400 solutions back out of the finished PDFs and compared them, square by square, with what was dealt. They match.

Which X Sudoku level should you print?

The levels differ only in how many digits are printed, but the gap in effort is far wider than the clue counts suggest. We ran all 100 puzzles of each book through a solver that knows one technique at a time:

Counts out of the 100 puzzles in each PDF: every puzzle, not a sample. Each counts once, under the hardest step it needed, from a solver that knows naked and hidden singles, locked candidates, naked pairs and triples, and the X-Wing, with the diagonals treated as houses. Puzzles in the last column still have exactly one answer.

Easy and Medium are the books to print for most people. Naked and hidden singles finish every Easy puzzle and 95 of the Medium ones. Hard is a coin toss: 52 fall to singles, but 41 need longer reasoning than locked candidates, naked pairs or the X-Wing. Expert is further again than its four fewer clues suggest, with 84 of 100 beyond all of them. Every one still has exactly one answer, but on paper they need full pencil marks and patience.

The diagonals also carry more of the load as the clues thin out. Ignore them, and 32 of the 100 Easy puzzles would still have exactly one answer; on Medium only 2 would, and on Hard and Expert none.

How do you start a diagonal sudoku on paper?

Look at the shaded squares first. Before you have written anything, a digit missing from a diagonal often has just one square left on it: we found one on all 100 Easy puzzles, 95 of the Medium, 83 of the Hard and 56 of the Expert. On Hard Puzzle 1 it is the 9 on the shaded line from top right to bottom left. Its three gaps are pencilled in here, and the two struck 9s are the squares a printed 9 rules out:

The 9 at R7C7 did its work twice, through its row and through its diagonal. That is the habit worth building on paper: a digit on a shaded square counts in four houses, its row, column, box and diagonal, and in the centre square, five. When you write one in, run your pencil along its diagonal straight away, because on paper nothing crosses the candidates off for you.

How should you print the X Sudoku PDFs?

At 100%, or “Actual size”. The pages are US Letter, and they print on A4 without losing anything: nothing on any page comes closer than 15 mm (0.6 in) to a side edge, and A4 is the taller sheet. Each puzzle grid is 11 cm (4.35 in) across, so every square is about 12 mm, room for small pencil marks in a 3 × 3 pattern. The solution grids are about 6 cm across.

• Puzzles only: pages 1 to 51. Puzzles 1 and 2 are on page 2, and Puzzles 99 and 100 on page 51.
• Answers only: pages 52 to 63. Puzzles 1 to 9 are on page 52, 10 to 18 on page 53, and so on to Puzzle 100, alone on page 63.
• Two-sided: print those as two jobs. Printed whole, page 52, the first answers, lands on the back of Puzzles 99 and 100.
• The shading is a pale grey, about 7% ink, so pencil shows over it. If a draft or toner-saving setting loses it, rule the two diagonals in lightly with a pencil.

Can you use X Sudoku PDFs in a classroom?

Yes, and the Easy book is the one to start with: singles finish every puzzle in it, and the rules fit in one sentence on the cover, which makes the cover a ready first handout or projector slide. Each puzzle page carries two puzzles, one for everyone and the second for whoever finishes first. Medium suits a group that already plays classic sudoku. Keep Hard and Expert for the keen few: with 41 and 84 of their 100 puzzles beyond the standard techniques, they make a poor whole-class exercise. For younger pupils, the 4×4 and 6×6 printables come first.

Puzzle numbers are printed above every grid and on every solution, so a class can work on “Puzzle 7” together, and a teacher’s copy of pages 52 to 63 is the whole answer key for one book.

How do you check your X Sudoku answers?

Find the puzzle’s number in the solutions at the back, nine to a page from page 52. The digits that were printed in the puzzle are bold there and the ones you had to find are in regular type, so the regular ones are all you need to compare.

Stuck halfway, and want to know whether what you have is right without seeing the rest? Type the printed digits and the ones you are sure of into the X Sudoku solver and press Step. If it fills in a square, every digit you typed is correct, again because there is only one answer. If it reports a repeated digit or that no solution exists, one of yours is wrong.