Well-being measurements are frequently used to support conclusions about a range of philosophically important issues. This is a problem, because we know too little about the intervals of the relevant scales. I argue that it is plausible that well-being measurements are non-linear, and that common beliefs that they are linear are not truth-tracking, so we are not justified in believing that well-being scales are linear. I then argue that this undermines common appeals to both hypothetical and actual well-being measurements; I first focus on the philosophical literature on prioritarianism and then discuss Kahneman’s Peak-End Rule as a systematic bias. Finally, I discuss general implications for research on well-being, and suggest a better way of representing scales.