This study sought to analyse, using the Mathematics Discourse in Instruction framework, teachers' explanatory talk when introducing standard units of length in standard 4 in Malawi. The study analysed teachers' use of content and pedagogical practices for introducing standard units of length and how that made the concept of standard units of length accessible to learners. Qualitative data was collected from two teachers from two rural schools in Malawi. Findings of the study showed that the teachers' explanatory talk included mathematical and non-mathematical language. The mathematical language included standard units of length, metre and centimetre, and the procedures for measuring and comparing lengths of objects. It was also observed that learners had access to the idea of measuring and comparing lengths of straight objects within their classrooms and were able to follow procedures for measuring lengths of objects in metres and centimetres. However, these findings also highlight the need for the teaching of length measurement that aims at providing opportunities to learners to develop the concept of units of length across varying dimensions and tasks. This study argues for the teaching of length measurement that emphasises on building learners' conceptual understanding of standard units of length.