Printable 6×6 Sudoku Puzzles

What is in each printable 6×6 Sudoku PDF?

There are four PDFs, one per level, and each holds 100 puzzles with their solutions. Every file is 63 US Letter pages, black and white, and about 300 KB:

• page 1 is a cover with the rules and the level;
• pages 2–51 hold the puzzles, two to a page, each grid about 4.3 inches (11 cm) across, so a square is roughly 18 mm wide;
• pages 52–63 hold the solutions, nine to a page in puzzle order.

The rules are those of 6×6 Sudoku: fill the grid so that every row, every column and every box holds the digits 1 to 6 once each. The boxes are two rows tall and three columns wide, marked by the heavy lines. Nothing on the page relies on colour, so a black-and-white printer loses nothing.

How were these 6×6 puzzles made and checked?

We dealt every puzzle with the generator that runs our online 6×6 game, seeded so that the same four PDFs can be rebuilt digit for digit. It fills a grid, takes clues away in random order aiming at 20, 16, 12 or 9, and puts a clue straight back if removing it would let a second answer in.

Then a separate solution counter, written for the printables and sharing no code with the generator, searched each of the 400 printed puzzles for a second answer. It tries every possibility rather than sampling, and it found none: every puzzle in these PDFs has exactly one answer. That is also what lets you check a finished grid without the key.

How do the Easy, Medium, Hard and Expert sheets differ?

Each level has four fewer clues than the one before, and Expert usually fewer still. On paper that changes how much you can fill at the first look and, from Hard on, which kind of single you need. We solved all 400 printed puzzles to measure it:

The exact puzzles in each PDF, each solved with the simplest technique available at every point. A square is “open at first look” if a naked or hidden single fills it before you write anything. The figures are medians; Expert puzzles have 24 to 27 empty squares. Pages: a cover, 50 of puzzles, 12 of solutions.

Easy and Medium never need more than a naked single: all 200 puzzles can be finished by finding a square that already sees five different digits, writing in the sixth and looking again. What changes is the pace. A typical Easy puzzle has 14 of its 16 empty squares ready at once, a Medium one 13 of 20, so on Medium more of the grid waits on your earlier answers.

Hard is where the step up is. Seven Hard puzzles have no naked single anywhere at the start, 14 need a hidden single at some point, and two need more. Expert puzzles have 9 clues (16 of them), 10 (59), 11 (24) or 12 (one): the generator stops short of 9 when no clue can go, and 97 of the 100 are minimal, so taking away any one clue would leave two answers. Fourteen Expert puzzles show no naked single at the start, and a third need a hidden single.

How do you start a 6×6 Sudoku on paper?

Start where the most digits meet. Take the fullest row, column or box, and for each empty square in it count the different digits it can see along its row, down its column and inside its box. At five, the sixth is the answer: write it in. This is the first move on Puzzle 1 of the Expert PDF, where only one square out of 25 qualifies:

That chain, one digit making the next square certain, is most of what solving a printed 6×6 involves. Expert Puzzle 1 needs nothing but naked singles from its first square to its last, and so do 347 of the 400 puzzles in the four PDFs.

When no square can see five digits, look at digits instead. Pick a digit, find a box that lacks it, and rule out every square of that box whose row or column already holds it; if one square is left, that is a hidden single. If you like pencil marks on Hard and Expert, an 18 mm square has room for them, kept small and in the same place every time.

Stuck on a Hard or Expert 6×6 puzzle?

Only six of the 400 puzzles need more than singles. Hard Puzzles 29 and 53 and Expert Puzzles 53 and 76 each need a one-digit chain such as the skyscraper, Expert Puzzle 72 needs an XY-Wing, and Expert Puzzle 4 is the sixth. On any other puzzle, if you are stuck, a single is waiting, usually a hidden one: go digit by digit through every box before you reach for anything harder.

Expert Puzzle 4, on page 3, is the hardest of the 400. Singles fill 9 squares and then stall with 17 open, and nothing our solver tries, up to an XY-Wing, moves it on. It still has exactly one answer, and on paper the way through is a test in pencil: choose a square with two candidates, write one in lightly and carry on with singles. From 13 of this board’s 14 two-candidate squares that settles it. The right digit runs on to the finished grid; the wrong one breaks within nine placements, leaving a square with no digit or a row or column with nowhere to put one. A contradiction proves the other digit, so this is logic, not luck.

How do you check your answers?

The solutions run in puzzle order, nine to a page: Puzzles 1–9 on page 52, 10–18 on page 53 and so on, with Puzzle 100 alone on page 63. For Puzzle n, divide n − 1 by 9, drop the remainder and add 52: Puzzle 55 is on page 58.

You may not need the key at all. Because each puzzle has exactly one answer, a full grid with no digit repeated in any row, column or box is the answer: there is no other it could be. Checking the six rows, six columns and six boxes for repeats takes a minute. Adding up is not enough: a correct row sums to 21, but so does 1, 2, 3, 3, 6, 6.

In class, that check can be the exercise. Print pages 2–51 and keep 52–63 back as the key: a grid that passes the repeat check is right, and a student who finds a repeat has to work out which of the two digits is wrong, and why.

How should you print them for home or class?

• A4 paper. The pages are US Letter. On A4, choose “Fit to page”: the sheet shrinks by about 3% and a square stays about 18 mm across.
• Only the puzzles you want. Puzzles 1 and 2 are on page 2, 3 and 4 on page 3, and so on: Puzzle n is on page n ÷ 2 + 1, rounded up.
• Half-sheets. Each page holds two puzzles, one above the other. Cut across the middle and each half carries one puzzle and its number, so 15 sheets give a class of 30 a different puzzle each.

For one puzzle to a page, or pages made for A4, the Sudoku generator builds 6×6 PDFs to order, with your choice of level, puzzles per page, paper size and answer key.

What should you print after 6×6?

If Easy is still a struggle, try the printable 4×4 Sudoku sets, which use the digits 1 to 4. If Expert stops needing a second look, move to classic 9×9 at Easy in the printable Sudoku collection. A 6×6 from a book or newspaper, if its boxes are 2×3, can go into the 6×6 Sudoku solver, which checks that it has one answer and solves it step by step. Teaching children? Start with Sudoku for Kids.