Health services researchers face two obstacles to sample size calculation: inaccessible, highly specialised or overly technical literature, and difficulty securing methodologists during the planning stages of research. The purpose of this article is to provide pragmatic sample size calculation guidance for researchers who are designing a health services study. We aimed to create a simplified and generalizable process for sample size calculation, by (1) summarising key factors and considerations in determining a sample size, (2) developing practical steps for researchers-illustrated by a case study and, (3) providing a list of resources to steer researchers to the next stage of their calculations. Health services researchers can use this guidance to improve their understanding of sample size calculation, and implement these steps in their research practice.