Population ageing is escalating rapidly now worldwide. This is an important time to determine if ageism or discrimination against older people is of concern, such as it being prevalent and/or increasing in prevalence. Over the years, many ageism measurement tools have been developed, with research findings from their use of prime consideration then for determining the prevalence of ageism and any prevalence trends. All print and open access English-language research articles published in 1953+ that used one or more ageism measurement tools in a study were sought using the Directory of Open Access Journals and EBSCO Discovery Service. A total of 25 ageism measurement tools were identified. However, only six had been used one or more times to measure the prevalence of ageism. The identified prevalence levels varied considerably, but most investigations using small convenience samples, with limited generalizability of findings. This paper highlights the need to continue developing ageism measurement tools to estimate ageism or use other measures, such as census and population representative polling, to assess the extent and impact of ageism. This foundational measurement is needed, as ageism could be prevalent and growing in effect.