Printable 16×16 Sudoku Puzzles

What is in each 16×16 PDF?

Four files, one per level, all built the same way. Each is a 126-page US Letter PDF of about 0.7 MB that opens straight from its download button, with no email and no signup:

• Page 1 is a cover with the rules and the level.
• Pages 2–101 hold Puzzles 1 to 100, one to a page. Each grid is 7 inches (17.8 cm) square, so a square is about 11 mm across, with roughly an inch and a half of clear paper above and below the grid for working.
• Pages 102–126 hold the answers, four to a page, in puzzle order.

The numbers are 1 to 16, printed in full, as the online 16×16 game shows them, rather than the 0 to 9 and A to F of hexadecimal puzzles (the style sometimes called Hexadoku). A 16 is one entry in one square, not a 1 and a 6. Every page is black and white, with heavy lines round the 4×4 boxes and nothing that depends on colour, and every page after the cover carries the level and its page number in the footer, so sheets from different files can be sorted back.

How do Easy, Medium, Hard and Expert differ?

Not mainly in how many numbers are printed. Easy always gives 120 of the 256; the other three all end up at about 94. That is because the generator removes numbers for as long as the level’s steps can still finish the board, and on a grid this size that runs out at about the same point whatever the steps are. What changes is what you need to finish.

All 100 puzzles in each PDF; every PDF is 126 pages. “Given” is the range of printed numbers, median in brackets. “Open at first look” is the median count of squares a single fills from the printed numbers alone, before you write anything, with the range. “Hardest step” is the hardest one our solver needed, trying the easier steps first, with the number of puzzles.

Which level should you print?

On paper, the steps up you feel are Easy to Medium, then Medium to Hard. Easy hands you about 22 squares the moment you start scanning, and it is the right first file even if 9×9 comes easily to you: what it trains is sweeping sixteen numbers across a board this size. Medium offers about 10 squares among 162 empty ones, so the opening is a hunt, but singles still finish every board.

Hard looks just like Medium on the page, with about the same count of givens, yet singles run dry early: on 99 of the 100 boards they stall after a median of 26 placements with about 135 squares still empty, and from there locked candidates, with singles, finish every one. Print it once you know that step. Expert stalls under singles on all 100 boards, and on 89 under locked candidates too, so it is for solvers who already look for pairs. None of the 400 needs anything past a naked pair or triple, and none needs a guess.

Does every puzzle have exactly one answer?

Yes, and we checked rather than assumed. We generated all 400 puzzles ourselves, with the same generator that deals the online game. It starts from a full grid and takes numbers out one at a time, keeping a removal only while the level’s own steps can still finish the board. Then a second program, the logic solver we wrote to test that generator and which shares none of its code, worked every printed puzzle from its givens with steps that never guess. It filled in all 400. A puzzle that logic alone can fill in has only one answer, and the answer key printed for it is that answer.

That is what makes the answer key worth having. With one answer, any square where your grid differs from the key is a mistake. On a puzzle with two answers you could finish a perfectly legal grid and still disagree with the key, and the PDFs that used to sit at these addresses carried exactly that risk. They came from our old generator, which blanked squares down to a fixed count and never checked what was left; tested later, 79 of 80 boards from it had more than one answer, and the 80th could not be shown to have one. The old files put two puzzles on a page, with squares about 7 mm across, so if your printout looks like that, download the file again.

Where do you start on a printed 16×16?

With a pencil and no notes. On a fresh sheet the quickest progress is cross-hatching: pick a box, pick a number it is missing, and run a light line along the row or column of every copy of that number that passes through it. If the lines cover every empty square of the box but one, the number goes in that one. This is how Puzzle 1 of the Easy file opens:

That is a hidden single, found without writing any notes. Puzzle 1 has 22 squares that a single fills at the start, 11 of them found by cross-hatching a box like this, and every number you write in shortens the next scan. On Easy and Medium the whole solve is that, repeated: sweep one number at a time across all sixteen boxes, then move to the next number.

On Hard and Expert the sweeps dry up, and that is the moment to start pencil marks. Mark only the box or line you are working on: an 11 mm square has room for a few small numbers, not sixteen. Then look for a number whose places in a box all fall in one row or column, and on Expert for two squares carrying the same two notes. The 16×16 game page draws both on real boards.

How should you print a 16×16 sudoku?

• Letter or A4, at full size. A4 is 6 mm narrower than Letter, but the grid has about 19 mm of margin on each side, so Actual size loses nothing; Fit shrinks the page by about 3% and works as well.
• One page to a sheet. Printing two pages per sheet shrinks the squares to about 7 mm, back to the cramped size of the old files.
• Print a range, not the file. Puzzle n is on page n + 1, so Puzzles 1–10 are pages 2–11. Print the answer pages separately, or not at all, and keep them out of sight while you solve.
• Pencil, and a fine one. A 0.5 mm lead keeps notes small enough to fit an 11 mm square and rubs out cleanly when a number turns out wrong.

How do you check your answers?

The answer grids are small, about 5.6 mm a square, so check one row at a time with a ruler or a folded sheet under it rather than reading across the whole grid. Because each puzzle has one answer, a square that differs from the key is wrong, and so may be everything you worked out from it: find the earliest wrong number, rub out back to it, and solve on from there rather than copying the rest. To check without seeing answers you have not reached, uncover a single box at a time.

Stuck rather than wrong? Every puzzle here can be finished by the steps in the table above, so the way on is a missed single or a locked candidate, not a guess. A 16×16 from another book or website is a different matter: if one will not come out, the 16×16 solver takes it typed in and says whether it has one answer at all.

Where to go next

To play on screen, with a wrong number marked the moment it goes in, the online 16×16 game deals fresh boards from the same generator (not these 400). For a shorter solve on paper, try printable 12×12 sudoku; for a longer one, printable 25×25 sudoku. The full printable sudoku collection has classic grids and other variants as PDFs too.