Function drives many early design considerations in product development, highlighting the importance of finding functionally similar examples when searching for sources of inspiration or evaluating designs against existing technology. However, it is difficult to capture what people consider to be functionally similar and therefore, if measures that compare function directly from the products themselves are meaningful. In this work, human evaluations of similarity are compared to computationally determined values, shedding light on how quantitative measures align with human perceptions of functional similarity. Human perception of functional similarity is considered at two levels of abstraction: (1) the high-level purpose of a product, and (2) a detailed view of how the product works. These human evaluations of similarity are quantified by crowdsourcing 1360 triplet ratings at each functional abstraction and creating low-dimensional embeddings from the triplets. The triplets and embeddings are then compared to similarity that is computed between functional models using six representative measures, including matching measures like cosine similarity and network-based measures like spectral distance. The outcomes demonstrate how different levels of abstraction and the fuzzy line between what is considered “highly similar” and “somewhat similar” may impact functional similarity representations by humans and subsequently affect how computed similarity aligns with these representations. The results inform how functional similarity can be leveraged by designers and therefore, applications lie in creativity support tools, such as those used for design-by-analogy, or future computational methods in design that incorporate product function.