The unemployment rate is commonly assumed to measure labour availability, but this ignores the fact that potential workers frequently come from outside the current set of labour market participants, the so-called inactive. The UK Longitudinal Labour Force Survey includes information that can be used to predict impending employment transitions. Using this unique dataset, new measures of labour availability, and indicators based on the more familiar unemployment rate alternatives, can be constructed and are reported here. The micro and macroeconomic performance of these labour force availability measures is compared. Two simplified models, which include several categories of reasons for not working as well as demographic variables, perform particularly well in all of the tests. The implications of these preferred models are further studied in the context of regional regressions and comparisons with alternative data sources. These results together illustrate the important role that some groups of the inactive can play as a source of potential workers.