---
title: "Bookshelf Calculator: Books per Shelf | Shelf Sonnet"
description: "How many books fit on a shelf, and how many shelves and bookcases your collection needs, from spine widths you measure or averages you can edit."
url: https://shelfsonnet.me/bookshelf-calculator/
---

Shelf space

# Bookshelf calculator

How many books fit on a shelf, and how many shelves does your collection need? Measure a shelf and a few spines, or start from averages you can change.

## How the shelves are counted

The calculator takes the inside width of one shelf, keeps the share you choose free for bookends, breathing room and new arrivals, and stands your books in it one by one: all the paperbacks, then the hardbacks, then the large books. A book never hangs over the end, so a shelf starts again when the next book will not fit.

**Measuring spines:** line up five to ten books of one kind, measure the whole row, and divide by the number of books, or measure each one and type the widths in. Paperback novels, hardbacks and art books differ a lot, which is why each has its own average. Leave 10 to 20% free if you plan to buy more.

Shelf height matters too: tall art books may not stand on a shelf meant for paperbacks, so measure the gap between shelves before you count them in.

## Questions

**How many books fit on a shelf?**

Divide the usable width by the average spine width. On an 80 cm shelf with 10% kept free, that is 28 paperbacks with 2.5 cm spines, or 20 hardbacks with 3.5 cm spines.

**Should I measure the inside or the outside of the bookcase?**

The inside: the space between the sides of the bookcase, or between the uprights of a wall shelf, is what the books have to fit in.

**Are the default spine widths accurate?**

They are only round starting numbers for this calculator. Books vary a great deal, so a few minutes with a ruler and your own books gives a much better answer.