When observing and trying to quantify the world around us, two simple facts can be appreciated and readily agreed upon. First, different physical quantities are characterized by different quantifiers, such as length and time. Second, objects come in different sizes. These two facts have far-reaching consequences that can be appreciated when we understand their mathematical implications and study the constraints that dimensions and size impose on physical processes. Obtaining information in this way is known as dimensional or scaling analysis. ‘Do you want to know a secret? Turkeys, giants, and atomic bombs’ considers several examples of scaling analysis and explains that dimensional analysis relies on a simple universal principle, the principle of dimensional homogeneity.