An estimated 55% of the global population live in cities, with this expected to increase to 70% by 2050. Thus, the strain from urbanisation generates issues like water pollution and land degradation leading to further social and environmental problems. Smart sustainable cities have been proposed as a possible solution but are a relatively new concept and are theoretically underdeveloped, and implementation applicability continues to be understudied. Despite the uncertainty around the idea, many cities globally have created distinctive visions of a smart, sustainable city. This paper developed a measurement instrument based upon a prior conceptualisation that embraced the subjective nature of the citizenry’s perceptions of a smart sustainable city. The measurement instrument was initially refined from a large statement list of 80 from the initial conceptualisation before statistically honing this instrument through exploratory factor analysis and confirmatory composite analysis. This is before applying the tool in the real-world context in various cities in Malaysia and UK. Known group validity was additionally used to verify the instrument, comparing between Malaysian and UK participants and between four different cities. A twenty-item measurement instrument consisting of four factors, Planning, Environment, Social and Smart, was developed from this study. These results support current theoretical perspectives with only minor variations from the core theory; however, this better reflects the dynamics of the smart sustainable city phenomenon.