Before buying a bookshelf there is always the same question, and almost never a number: how many books will go on it? Libraries know, because they build with it. For the home we have done the maths, with the dimensions of the book formats, the paper thickness from the manufacturer and the grid of our shelf. Two things come out: a number per board, and a limit that is set not by width but by weight.
How wide a book is
A book spine is paper, halved and stacked. One sheet carries two pages, so the spine is half the page count times the sheet thickness, plus the cover. The sheet thickness is in the paper manufacturer's data sheet: a common book paper of 80 grams per square metre is 120 micrometres thick, one of 90 grams 135, a coated art-book paper of 150 grams 225. A paperback with 300 pages therefore has a spine of 18 millimetres, a bound non-fiction book with 350 pages 28, a textbook with 400 pages in the 17 × 24 format a good 31, an art book with 200 pages 26. The cover comes on top: half a millimetre for the paperback, around four for the hardcover.
How many fit on a board
Between the posts of a KUUDU board there are 69.5 centimetres. Divided by the spine, that is 37 paperbacks, 24 bound non-fiction books, 22 textbooks or 26 art books. Per metre: 53 paperbacks, 35 non-fiction, 32 textbooks. Libraries plan more cautiously, with 20 to 30 bound volumes per metre; they reckon with thicker volumes and with air for pulling them out. If you want to estimate your own collection, 30 books per metre is rarely wrong.
What they weigh
The weight follows the same calculation: half the page count times sheet area times grammage, plus the cover. The paperback comes to 300 grams, the non-fiction book to 550, the textbook to 900, the art book to 1.6 kilos. And now the limit: a KUUDU board carries 20 kilos. 37 paperbacks weigh eleven, 24 non-fiction books thirteen, 22 textbooks just under twenty. 26 art books would be 42 kilos. So a board takes twelve at most, and then it looks half empty. That is the sentence to know before an art-book shelf: with large formats the board is full before it looks full.
Four book formats on a KUUDU board with 69.5 cm of clear width. Formats after epubli, sheet thicknesses after the Munken Print White data sheet (Arctic Paper); page counts and cover weights are assumptions of this calculation and are stated in the table. Weight = pages ÷ 2 × sheet area × grammage + cover.
| Format |
Assumption |
Spine |
Weight |
Side by side per board |
Kilos per board |
Maximum at 20 kg |
| Paperback 12.5 × 19 cm |
300 pages, 80 g, cover 15 g |
18.5 mm |
0.3 kg |
37 |
11 |
37 |
| Bound non-fiction 13.5 × 20.5 cm |
350 pages, 90 g, cover 110 g |
28 mm |
0.55 kg |
24 |
13 |
24 |
| Textbook 17 × 24 cm |
400 pages, 90 g, cover 170 g |
31 mm |
0.9 kg |
22 |
20 |
22 |
| Art book 30 × 29.4 cm |
200 pages, 150 g, cover 280 g |
26.5 mm |
1.6 kg |
26 |
42 |
12 |
From the collection to the wall
With the number per board, the collection becomes a wall. 500 paperbacks need 14 boards, that is two sections of seven levels each: one and a half metres wide, 1.72 metres tall. 1,000 paperbacks need 27 boards, four sections of seven levels, three metres of wall. 2,000 is the wall twice over or the levels up to the ceiling; from there the article on shelf heights helps, because the upper rows then lie in the stretch zone. Bound books need one and a half times as much for the same number: 1,000 non-fiction books are 42 boards, six sections, four and a half metres.
The gap height is simple. Paperbacks and non-fiction stand in the 25 gap with air, textbooks in the 17 × 24 format fit with one centimetre to spare, the next gap up is better, and art books need 35. If you sort your collection by height instead of sizing every row for the tallest book, you gain a whole level on one wall; how libraries do it is in the article on libraries.
And the weight of the wall, not just of the board: four sections with seven levels of paperbacks are around 310 kilos, the same wall with non-fiction 370, the shelf itself not counted. Libraries plan their open-access areas at six kilonewtons per square metre, 600 kilos. A bookshelf on a living-room wall is not a stack room, but on a timber beam ceiling in an old building a full wall of books is a question for someone who calculates ceilings, not for a furniture page.
What this means for planning
Count first, then calculate, then build: estimate the books by format, translate them into boards with the table, and for art books take the weight, not the width. The living-room bookshelf page and the ceiling-high shelf page show configurations that came about this way, and in the configurator you see the height of every level while you build. How deep the boards need to be for which formats is in the article on shelf depths.
Sources
- Book formats: epubli, "Buchausstattung: Alle Formate, Bindungen & Papiere" (paperback 12.5 × 19, non-fiction 13.5 × 20.5, academic 17 × 24, art book 30 × 29.4 cm; book block papers 80–90 g/m² uncoated, 140–150 g/m² coated). epubli.com, retrieved 11 September 2026.
- Sheet thicknesses: Arctic Paper, data sheet Munken Print White 15 (bulk 1.5): 80 g/m² 120 µm, 90 g/m² 135 µm, 150 g/m² 225 µm. igepa.de (PDF), retrieved 14 September 2026. Spine formula pages ÷ 2 × sheet thickness plus 0.3–0.6 mm softcover or around 4 mm hardcover: danielreiche.de, retrieved 14 September 2026.
- Library planning: Berufsverband Information Bibliothek, OPL checklist 35 "Bauplanung von Firmenbibliotheken in Zahlen" (Martina Kuth), values from DIN-Fachbericht 13 (2009): 20 to 30 bound volumes per running metre of shelf; shelf depth for octavo and quarto 250 to 300 mm; floor load for open-access areas with reading space 6 kN/m². bib-info.de (PDF), retrieved 14 September 2026.
- KUUDU dimensions: configurator constants (board 75 cm, posts Ø 1.5 cm with centre 2 cm from the edge, clear width 69.5 cm; gaps 25 and 35 cm; board 1.6 cm; foot 10 cm, cap 1 cm). Load 20 kg per board according to the product information. Cover weights and page counts in the table are assumptions of this calculation.
