Studies of tardigrade biology have been severely limited by the sparsity of appropriate quantitative techniques, informative on a single-organism level. Therefore, many studies rely on motility-based survival scoring and quantifying reproductive success. Measurements of O2 respiration rates, as an integrating expression of the metabolic activity of single tardigrades, would provide a more comprehensive insight into how an individual tardigrade is responding to specific environmental factors or changes in life stages. Here, we present and validate a new method for determining the O2 respiration rate (nmol O2 mg-1 h-1) of single tardigrades under steady state, using O2 microsensors. As an example, we show that the O2 respiration rate determined in MilliQ water for individuals of Richtersius coronifer and of Macrobiotus macrocalix at 22°C was 10.8±1.84 and 13.1±2.19 nmol O2 mg-1 h-1, respectively.