The size of Mandemar is approximately 20.2 square kilometres. The population of Mandemar in 2011 was 388 people. By 2016 the population was 56 showing a population decline of 85.6% in the area during that time. The predominant age group in Mandemar is 40-49 years. Households in Mandemar are primarily childless couples and are likely to be repaying over $4000 per month on mortgage repayments. In general, people in Mandemar work in a trades occupation. In 2011, 79% of the homes in Mandemar were owner-occupied compared with 109.5% in 2016.