Feature-based methods are commonly used to explain model predictions, but often assume interpretable features are readily available.The FIX benchmark, called Features Interpretable to eXperts, aims to measure how well a collection of features aligns with expert knowledge.FIXScore is proposed as a unified expert alignment measure applicable to diverse real-world settings across different domains and data modalities.Popular feature-based explanation methods perform poorly in terms of alignment with expert-specified knowledge, signaling the need for better methods.