Perceived clutter is a potentially important but understudied construct in UX research. In this paper we described the development and assessment of a standardized questionnaire for reliable and valid measurement of perceived clutter of websites. Starting with an initial set of 16 items and two hypothesized factors, a series of exploratory analyses led to a final set of five items, two for the hypothesized construct of Content Clutter (too much irrelevant content like ads and videos) and three for the hypothesized construct of Design Clutter (poor design of relevant information like too much text, an unpleasant layout, or too much visual noise). Confirmatory analyses using an independent dataset showed excellent fit statistics for CFA of the five-item questionnaire and good fit for an SEM of the connections between clutter and other UX constructs. Researchers should exercise caution about generalizing results to other contexts and interfaces, but UX practitioners should be able to use this perceived clutter of websites (PCW) questionnaire when assessing consumer websites.