© 2018 John Wiley & Sons Ltd. Type design and typography have always been about usability: an unreadable document is not usable. Digital type brought a new flexibility to print and screen design, but the full effects of this have yet to be worked through. The fluid circumstances in which digital type is used mean that people need to remain aware of how applying simple rules in the appropriate circumstances can be used to improve the contribution of digital type to human-computer interaction (HCI). An understanding of usability and measurement can help improve the quality of documents, and also reveal where there is still scope for more work. In particular, measurement of the usability of size and shape decisions in digital typography must take into account the growing need to repurpose published material-to recast it from a book into an eBook, or from a thesis into a Web site, or from a Web site into a printed brochure.