This article reports on the development of a scale for measuring the self-regulated motivation for improving speaking English as a foreign language (EFL). The scale, which is informed by Pintrich's self-regulated learning (SRL) model, addresses motivational aspects of SRL. The scale was constructed in three stages: item pooling, exploratory factor analysis and confirmatory factor analysis. A total of 1065 learners participated in the research. Exploratory and confirmatory factor analyses were carried out using SPSS and structural equation modelling respectively. The findings led to the development of a 20-item scale that involved four factors: (a) task value activation, (b) regulation of learning environment, (c) regulation of affect and (d) regulation of classroom environment. This factor structure indicates that developing positive affective reactions, enhancing interest in the task and developing positive perceptions of task value are important for developing EFL speaking skills. The research also revealed that changing both in-class and out-of-class environments is important for self-regulated learners as this creates more opportunities to practise spoken language.