Large print sudoku for seniors: what to look for, in millimetres

Large print may suit people who can still read print but find regular print hard work. RNIB, the Royal National Institute of Blind People in the UK, puts it this way: "If you have some vision but you struggle to read regular print, large or giant print may be for you." In sudoku two sizes count: the printed digits, which you read one at a time with no word around them to help you guess, and the empty squares, where you write your own digits in pencil.

If you are choosing a sudoku book as a Christmas present for a parent or grandparent, or for yourself, the words "large print" on the cover do not say how large. We measured what they mean in one book, our own Extra Large Print Sudoku for Seniors, and set the numbers next to two published guidelines. Both guidelines were read, and the interior PDFs of the book measured, on 3 November 2026. We measured the files, not a printed copy.

The short version#

• Large print is generally 16 to 18 point in RNIB's words, and regular print is usually 10 or 12. UKAAF, the UK Association for Accessible Formats, asks for at least 16 point for large print, ideally 18.
• The puzzle digits in our book are 32.85 point, bold, 2.05 times UKAAF's minimum. Measured on the ink, they are 7.73 to 8.02 mm tall.
• The squares are 19.98 mm wide, about 2 cm, with one puzzle per page.
• Every puzzle has exactly one answer. Two separate programs counted the solutions of all 120 puzzles, read back from the PDF, and found one each: the answer printed at the back.
• Nothing in the book is smaller than 16 point, the UKAAF minimum.

What to look for#

1. Big digits. If a book gives its point size, set it next to the guidelines: 16 is the large print minimum to UKAAF, 18 the ideal. Our puzzle digits are 32.85 point.
2. Big squares, not only big digits. You write in the squares. Ours are 19.98 mm across, and a printed digit fills about 39 % of the height of its square, which leaves about 6 mm of white paper above and below it.
3. Box lines that stand out. The nine 3 x 3 boxes are part of the rules, so their borders should be easy to tell from the lines between squares. In our book the box borders and the outer border are 2.2 point (0.78 mm), and the lines between squares 0.75 point (0.26 mm).
4. One puzzle per page. Each of our 120 puzzles has a page to itself, and the grid is 7.08 in (179.8 mm) square, 83 % of the page width.
5. Levels that grow. Ours runs from 40 easy puzzles to 40 medium to 40 hard, with the level printed on every puzzle page. More on what the levels mean below.
6. Exactly one answer, and the answers at the back. A sudoku with two answers cannot be finished by logic alone: at some point you have to guess. How we checked ours is below, too.

Points are not millimetres#

A point is 1/72 of an inch, and the point size measures the whole body of the type, not the digit you see. How much of it the digits fill depends on the typeface. In the typeface of our puzzle digits, Atkinson Hyperlegible Bold, the capitals are 0.668 of the point size: 7.74 mm at 32.85 point, by the font file.

So millimetres say more. We rendered all 3,764 printed digits of the 120 puzzles at 1200 dpi and measured their ink: every one is 7.73 to 8.02 mm tall. The middle values are 7.73 mm for 1, 4 and 7, 7.87 mm for 2, 5 and 9, and 8.02 mm for 3, 6 and 8. The same digits at 12 point, the top of RNIB's regular print, would be 2.88 mm tall; at 18 point, the top of its large print range, 4.31 mm. The puzzle digits are 2.74 times the size of 12-point print in the same typeface.

The measurements come from the interior PDF of the paperback, whose pages are 8.5 x 11 in, the book's trim size, so the millimetres are those of the page at full size.

What we measured in the book#

• Puzzle digits: 32.85-point bold, black, in Atkinson Hyperlegible, a typeface from the Braille Institute (the font file names it as the maker), 7.73 to 8.02 mm tall on the ink.
• The grid: one per page on 120 pages, 7.08 in (179.8 mm) square, with squares 19.98 mm wide. Box borders and the outer border 2.2 point (0.78 mm), lines between squares 0.75 point (0.26 mm).
• Headings: "Puzzle 1" to "Puzzle 120" in 17 point, and the level, "Easy", "Medium" or "Hard", in 16 point.
• Answers: at the back, four grids a page on 30 pages, in 16-point digits (3.83 mm tall on the ink) in squares 9.70 mm wide. The digits a puzzle starts with are bold and black; the ones you fill in are regular and grey, so you can tell the two apart.
• Other pages: a how-to page with the rules in 18 point, and a notes page between the puzzles and the answers.
• Smallest text: 16 point, for the answers with their headings, the page numbers, the level labels and the copyright page. None of the five fonts in the file is italic.
• Margins, measured to the nearest ink on every page: 0.50 in to the outer side edge, at least 0.76 in to the spine side on the puzzle pages, and 0.32 in to the bottom edge.

What the levels mean#

Puzzles 1 to 40 are easy, 41 to 80 medium and 81 to 120 hard. The how-to page promises: "You can solve every puzzle by logic, with no guessing; the hard ones near the end need more than the basics." We checked that with a small logic solver of our own.

• Easy puzzles start with 37 or 38 of the 81 squares filled in, medium ones with 29 or 30, hard ones with 23 to 31 (26 in the middle).
• Every easy and every medium puzzle can be finished with singles alone: a square where only one digit fits, or a digit with only one place left in a row, column or box.
• None of the 40 hard puzzles can be finished with singles alone. Each needs at least one harder step, and the solver finished all 40 once it could also use locked candidates (inside a box, a digit can only go in one row or column, so it is ruled out from the rest of that row or column, or the other way round) and pairs (two squares in a row, column or box that can only hold the same two digits, or two digits that can only go in the same two squares). It never had to guess.

So the number of starting digits is not the whole story: a hard puzzle can start with 31 digits, more than any medium one, and still need the harder steps.

Exactly one answer, checked#

We did not take the puzzle generator's word for it. We read the digits of all 120 puzzles and all 120 answer grids back out of the paperback's PDF, by their place in the drawn grid, and checked them:

• every answer grid is a full, valid sudoku, and its bold digits are exactly the puzzle's digits;
• two separate solution counters, one that tries digits square by square and one using Knuth's Algorithm X, each found exactly one solution for all 120 puzzles;
• in all 120, that solution is the answer printed at the back.

The hardcover's PDF passed the same checks.

How that compares with the guidelines#

UKAAF's minimum standards for clear and large print (document MS03, June 2012) are a checklist. Against it:

• Text size: UKAAF asks for a "Minimum text size of 16 point for large print, ideally minimum of 18 point". The puzzle digits are 32.85 point, 1.83 times the ideal, and the how-to page is 18, the ideal. The answers, page numbers, level labels and the copyright page are 16: the minimum, not the ideal.
• Page numbers and labels: UKAAF would have them ideally the same size as the body text. Ours are 16 point, next to 18 on the how-to page and 32.85 in the grids.
• Italics: it asks for none, and there are none.
• Capital letters: it asks for no large blocks of capitals, and there are none: no word of four letters or more in the book is set all in capitals.
• Contrast: the puzzle digits and the grid lines are black, on white paper. Dark grey (#6B6B6B) is used for the page numbers, the level labels, the subtitle on the title page, the subheadings of the answer pages, the copyright page and the filled-in digits of the answer grids.
• Typeface: UKAAF names Arial as an example of a legible typeface. The digits here are set in Atkinson Hyperlegible, the rules in Lato.
• Cover: it asks for a cover that is not glossy. The paperback's cover is matte.

RNIB's page on large and giant print gives a range, not a checklist: "Large print is generally 16 to 18 point size. Giant print is anything larger than this." By that measure the how-to page is large print, at the top of the range, and the puzzle digits, at 32.85 point, are larger still: what RNIB calls giant print.

If you make large print sudoku books#

What measuring our own book taught us:

1. Size the digits from the square. Big digits in small squares leave no room to write. Ours fill about 39 % of the square's height.
2. Measure the ink, not only the point size. The same point size gives different heights in different typefaces; a render at 1200 dpi tells you the height on the page.
3. Use two line weights. Ours are 2.2 point for the boxes and 0.75 point between squares.
4. Check the file you upload. Read the digits back out of the final PDF and count the solutions with two separate programs; compare each solution with the printed answer.
5. Grade by the steps a solver needs. In our book the starting digits of medium (29 to 30) and hard (23 to 31) puzzles overlap; the steps needed do not.
6. Watch the small text. In our book the page numbers, the labels, the answers and the copyright page are the text at the 16-point minimum.

Our book#

Extra Large Print Sudoku for Seniors, by E. M. Linden, is our own book, and the one measured here: 120 puzzles, 40 easy, 40 medium and 40 hard, one per page, with a how-to page, a notes page and full answers, 154 pages.

• Paperback, 8.5 x 11 in: amazon.com/dp/B0HP96VPK1
• Hardcover, 8.25 x 11 in: amazon.com/dp/B0HPBYY4X2. Its interior PDF holds the same 120 puzzles and answers at the same levels; on a page 0.25 in narrower, the grid is 6.84 in (173.7 mm) square, with squares 19.30 mm wide and 31.74-point digits, 7.49 to 7.75 mm tall.

See the price on Amazon. The front cover picture was made with an AI image tool. The how-to page, the back cover text and the description were written with an AI writing tool. The puzzles, solutions, layout and the cover type are made by ordinary computer programs.

If you make puzzle books, our sudoku book maker has large print on by default: bigger grids and digits, fewer puzzles per page.