Anaemia is a serious global public health problem that particularly affects young children, menstruating adolescent girls and women, and pregnant and postpartum women. It is a condition in which the number of red blood cells or the haemoglobin concentration within them is lower than normal, affecting the blood’s ability to carry oxygen to the body’s tissues. To reliably monitor the prevalence of anaemia at a population level, it is vital to measure the haemoglobin concentration in an accurate and precise way. In large-scale surveys, however, haemoglobin is most commonly measured using single-drop capillary blood specimens in point-of-care devices. Emerging evidence suggests that the use of single-drop capillary blood can introduce random and/or systematic errors, which may lead to inaccurate estimates, complicating effective anaemia programming. This technical brief describes the current best practices for haemoglobin measurement, providing guidance to help plan or implement field surveys to assess anaemia at a population level. Continuing work to review emerging evidence is led by members of the WHO-UNICEF Technical Expert Advisory group on nutrition Monitoring (TEAM).