Bulk

Micrometer with digital display

Bulk is a term used to describe the thickness of paper stock. The bulk of a book is determined by the bulk of the paper, along with the total number of pages. Bulk needs to be considered for the size, weight, binding, and handling of a book.

Bulk can be measured by this formula:

bulk = (thickness in mm / weight in grams per square metre ) x 1,000  

A higher bulk paper:

• feels softer and thicker
• is lighter in relation to its thickness
• is used widely in novels often referred to ‘bulky’ book paper e.g. ‘bulky paperback’

A lower bulk paper:

• feels denser and thinner
• is common in gloss magazines and coated art paper

Bulk is important in book publishing because higher bulk paper is often associated with lower quality books.

PUBLISHING TIP – If you have an example of a paper but don’t know what thickness it is you can measure it with a micrometer. A micrometer measures ums or one thousandth of a millimetre or 0.001 mm. An um is also known as a micron.