Amphibians, like other ectotherms, must balance conflicting demands for energy expenditure, physiological processes, and behaviour in response to environmental temperature variations that influence their survival and reproduction. Understanding these dynamics is crucial for assessing amphibians' resilience to climate change and identifying the stressors they face in their thermal environments. Our study investigated the influence of ambient temperature (T_a) on resting metabolic rate (RMR) in adult Rana temporaria and how the frogs' thermoregulatory reality in the field (field body temperature, T_b) while being active aligns with their responses to a wider range of temperatures in a thermal gradient (preferred temperature, T_pref). As anticipated for ectotherms, the RMR increased with T_a, doubling with each 10 °C increment, in accordance with the Q₁₀ coefficient. Consequently, absolute changes in RMR increased with increasing temperature. In the thermal gradient experiment, frogs primarily selected temperatures around 25 °C. At this temperature, which is not too far from the critical maximum temperature (CT_max) of 30 °C, RMR was 0.106 mL O2 g⁻¹ h⁻¹. The mismatch between actual field T_b and laboratory T_pref highlights the constraining influence of other environmental factors such as favourable microhabitat availability or hygric conditions. This study suggests an effective balance between energy requirements and thermoregulatory behaviour in R. temporaria , if favourable conditions are available. However, it also shows that the environmental reality of animals often deviates from unimpeded preferences of active individuals and thus results from experimental procedures might not necessarily reflect the situation in the field.