Printable 25×25 Sudoku Puzzles

What is in these 25×25 sudoku PDFs?

There are four files, one per level, and each holds 100 puzzles on 151 US Letter pages: the rules on the cover, one puzzle to a page on pages 2 to 101, and the solutions two to a page on pages 102 to 151. Each grid is 25 squares by 25, split by heavy lines into twenty-five 5×5 boxes, and every row, column and box must hold the numbers 1 to 25 once each. The pages are black on white with no shading, so a black-and-white printer loses nothing.

Puzzle 1 is on page 2, so Puzzle n is always on page n + 1: that is the page number to type into the print dialog when you want one puzzle rather than the whole file. Each file is about 1.7 MB.

How do Easy, Medium, Hard and Expert differ?

Less than you might expect in how many numbers are printed. Easy gives 325 of the 625, just over half; Medium, Hard and Expert all give about 264, a little over 40%, and their ranges overlap almost completely. What changes is the hardest step you need once the obvious placements run out. We ran every printed puzzle through a solver that always tries the simplest step first, and the levels separate cleanly:

All 100 puzzles in each PDF, exactly as printed. The solver tries naked and hidden singles, then locked candidates, then naked pairs and triples, then the X-Wing, and it never needed the X-Wing.

Easy and Medium never need more than singles: a square with only one number left (a naked single), or a number with only one place left in a row, column or box (a hidden single). Medium gives you about 60 fewer numbers to start from, so the singles take longer to find. On Hard they run out early on every puzzle: on Hard Puzzle 1 they fill 50 of the 366 empty squares and stop, and the next step is locked candidates. Expert goes one step further: on every Expert puzzle there comes a point where singles and locked candidates have both run out, and the way on is a naked pair or naked triple. On Expert Puzzle 1 that point comes with 302 squares still empty. No puzzle in any of the four files needs a guess.

Does every 25×25 puzzle here have one solution?

Yes, and because we made them we can say how we know. Every puzzle in the four files was dealt by the generator behind our online 25×25 game, with a fixed seed. The generator removes numbers in a random order and keeps a removal only while the level’s own steps can still finish the board: singles for Easy and Medium, singles and locked candidates for Hard, and naked pairs as well for Expert. Easy stops at 325 numbers; the other three remove numbers until those steps cannot spare another.

Each puzzle was then checked by a second solver, written separately from the generator, that only ever rules out a number that cannot go. A puzzle it can fill completely has exactly one answer, and that answer must match the one printed at the back.

If you have an older printout from this page with two puzzles to a sheet, it came from an earlier script that blanked squares to a fixed count and never checked what was left. When we tested the generator it used, not one of 80 boards could be shown to have exactly one answer, and 67 had more than one, so a puzzle from those sheets that left you stuck may have had no logical way through. These links now serve the new files.

How do you start a 25×25 sudoku on paper?

Work one band at a time. A band is five boxes side by side, sharing five rows. Each number appears five times in a band, once in each box and once in each row, so the five boxes hold it in five different rows. When four boxes of a band already show a number, they show it in four different rows, and the fifth box has to take it in the row that is left. Here it is on Puzzle 1 of the Expert file, as printed:

On paper, take one number at a time along each band, then down each stack of five boxes, where the columns work the same way. A strip of paper laid along the bottom of a band keeps your eye in its five rows, only 1.4 inches tall on the printed page.

That is a single, as hard as anything Easy or Medium asks. For what comes after the singles on Hard and Expert, the 25×25 game page works through locked candidates and a naked pair with diagrams, and our guide to pencil marks covers keeping notes you can still read after a break.

What paper size is best for a 25×25 sudoku?

The files are US Letter. Printed at actual size (100%), the grid is 7 inches (178 mm) across, each square is 0.28 inches (7.1 mm) wide, and the given numbers are in 11-point type. That fits on A4 too: A4 is 210 mm wide, so printing at 100% keeps the whole grid, and “fit to page” shrinks it by only 3%.

• For bigger squares, print on Tabloid or A3 with “fit to page” on. The grid grows to close to 9 inches across on Tabloid (11×17 in) and about 240 mm on A3, so each square is about 9 mm instead of 7.
• Legal paper gains nothing. It is the same width as Letter, so the grid stays 7 inches wide.
• Print one puzzle at a time. The whole file is 151 sheets single-sided; for Puzzle n, print page n + 1 only.
• Keep notes small and few. A 7 mm square has room for two or three small notes, not twenty-five. Note a square once it is down to a few numbers, and write in its corners so the middle stays free for the answer.

Where are the answers, and how do you check them?

The solutions start on page 102, two to a page: Puzzles 1 and 2 on page 102, Puzzles 3 and 4 on page 103, and so on to Puzzles 99 and 100 on page 151. For Puzzle n, the solution is on page 101 + n/2, rounded up: Puzzle 37 is on page 38, and its solution on page 120.

Each solution grid is half the width of a puzzle, so its squares are about 3.5 mm and its numbers small; the PDF on screen, zoomed in, is easier to read than the printed page, and it keeps the answers out of sight until you want them. Check a box at a time rather than reading the whole grid. If a number is wrong, rub out anything you placed because of it as well, not just the one square.

Where can you find more large sudoku?

To play a 25×25 on screen, our 25×25 game deals a fresh board from the same generator at the same four levels, marks a wrong number the moment you enter it, and saves your place between sittings. For something smaller on paper, the printable 16×16 sudoku has 4×4 boxes on 256 squares, the printable 12×12 sudoku has boxes three rows tall and four columns wide, and the printable sudoku collection has the rest.