The question turns up in two very different places. On r/IKEA, people ask how many books a BILLY holds before they buy three. In math homework, it's "a bookshelf is 4-3/4 feet wide; how many 3-inch-wide books will fit?" Both use the same arithmetic, so let's do both.
Short answer: plan on about 10 average books per linear foot of shelf when packed tight, and about 7 per foot if you want room for bookends and decor. A 36-inch shelf holds about 30 books packed, or 21 styled.
Where "10 per foot" comes from
An average book is a bit over an inch thick. Mass-market paperbacks are thinner and big hardcovers fatter, so a mixed shelf averages about 1.2 inches per book. That's roughly 0.83 books per inch, or 10 per foot.
Adjust for what you own:
| Collection | Avg. thickness | Books per foot |
|---|---|---|
| Mass-market paperbacks | ~1 in | 12–14 |
| Mixed fiction (paperback + hardcover) | ~1.2 in | ~10 |
| Hardcovers | 1.5–2 in | 6–8 |
| Art and coffee-table books | 1–1.5 in, but deep | 8–10 (lying flat, in stacks) |
The formula
Books = shelf width (in) ÷ average book thickness (in)
Then multiply by the number of shelves. If you want styled shelves rather than a library wall, multiply by 0.7. That leaves about 30% for objects, plants and breathing room, which is what most designers aim for.
Our Bookshelf Capacity Calculator does this for any width and shelf count, with a packed or styled option.
Worked examples
The homework question: 4-3/4 ft shelf, 3-inch books
Convert to inches first: 4.75 × 12 = 57 inches. Then 57 ÷ 3 = 19 books. (If you got 14¼, you probably divided feet by inches without converting.)
The paperback question: 40 copies on 5 ft, how many on 8 ft?
40 ÷ 5 = 8 books per foot, so 8 × 8 = 64 copies.
An 80 cm (31.5 in) bookcase, 6 shelves
Packed: 31.5 × 0.83 ≈ 26 books per shelf, × 6 = about 156 books. Styled: about 18 per shelf, or about 110. That's the size of a standard IKEA BILLY. The Reddit guess of "40 per shelf" only works with thin paperbacks.
A wall of shelving, 10 ft wide, 5 shelves
That's 50 linear feet of shelf, so about 500 books packed or 350 styled.
Don't forget weight and spacing
- Books weigh about 20–30 lb per linear foot. A full 36-inch shelf can carry 60–90 pounds, which is why particleboard shelves sag in the middle. Use thicker shelves, a center support, or shorter spans for heavy collections.
- Keep the heaviest books low on tall bookcases, and anchor tall units to the wall. Always.
- Space shelves 11–13 inches apart for standard books and 14–16 inches for oversized ones. Our shelf spacing calculator works it out for your wall. For wall-mounted shelves, check the floating shelf capacity calculator before loading them.
Making a full bookcase look good
A fully packed bookcase is great for readers and less great in a living room. A few tricks from people who post their shelves on r/bookshelf:
- Mix vertical rows with horizontal stacks, which double as bookends.
- Group by color or by size for a calmer look. Group by genre if you actually need to find things.
- Leave one object per shelf (a plant, a small frame, a bowl) to break up long runs of spines.
- Push books to the front edge of the shelf, not the back. They look tidier and you lose the dust line.
If you're planning a reading corner around those shelves, see reading nook ideas, or upload a photo of the room to the AI room designer to try layouts before you build anything.
Frequently asked questions
How many books fit on a 3 foot shelf?
About 30 average books packed tightly, or around 21 if you leave room for decor.
How many books per linear foot of shelf?
About 10 for a mixed collection, 12–14 for paperbacks and 6–8 for hardcovers.
How many books can a bookshelf hold?
Multiply the shelf width in inches by 0.83, then by the number of shelves. A 31.5-inch, 6-shelf bookcase holds about 156 books packed.
How much do books weigh per foot?
About 20–30 pounds per linear foot, depending on paper and binding.