The European Union and various individual countries strive for a more circular economy to reduce environmental pressure. The transition towards a circular economy requires a change in what and how we consume. We argue that a realistic estimation of the environmental mitigation potential depends on 1) the environmental benefit that results from a certain circular behaviour, referred to as the ‘theoretical reduction potential’ (TRP), and 2) the behavioural plasticity, reflecting the share of consumers who are not yet engaging in the behaviour but would be willing to do so if circular goods and services are easily accessible and affordable. The aim of this study was to provide insight into the environmental mitigation potential of circular consumer behaviour by assessing both their TRP and behavioural plasticity. To do so, we conducted a large-scale survey in the Netherlands (n = 2542) in which we examined the current adoption rate and willingness of consumers to engage in 92 circular consumer behaviours. Furthermore, we made a rough estimate of the TRP of these behaviours in terms of greenhouse gas emissions and land use. Our results show that many behaviours with a large TRP (mainly related to consuming less and saving energy) have a rather low behavioural plasticity, either because most consumers are not willing to adopt such a behaviour or because they are already engaging in it. Behavioural plasticity is relatively high when it comes to prolonging product lifetimes and purchasing more sustainable product alternatives, but these behaviours tend to have a relatively small TRP. Our findings demonstrate that the TRP is a limited indicator of the actual environmental mitigation potential of circular consumer behaviour and suggest that behavioural plasticity is an important additional indicator to identify the types of behaviour relevant for research and policymaking.