Subscribe to The Chicago Manual of Style Online
Usage and Grammar
Q. We are editing a book on global climate change to be published in the United States. What is the convention regarding using metric terms in US books? Should the US equivalents appear along with the metric? Or should all measures be converted to US? If we do convert, should we spell out the English measures?
A. Don’t worry about a convention; you should decide what works best for your readers. US readers will appreciate converted measures, but since the metric measures are already there, and you have a potentially global readership, you might as well supply both.