Eco-efficiency is often considered an adequate response to the problem of the scarcity of non-renewable resources. Even if a more eco-efficient use of natural resources cannot guarantee lower resource consumption, it can allow a better combination of desirable economic activity with undesirable resource use. However, more eco-efficient use of resources at the micro-level does not always lead to higher eco-efficiency at the macro-level. This is due to resource flows between actors at the micro-level. They use both virgin resources and resources that have been previously used. Virgin resources represent the relevant scarcity at the macro-level, while eco-efficiency at the micro-level typically does not discriminate between virgin and used resources. We develop an eco-efficiency formula that closes this gap. Our formula not only allows the measurement of the eco-efficiency of virgin resource use at the micro-level, but also helps to identify the drivers of the eco-efficiency of virgin resource use. Application of the formula to the case of gold in smartphones points to the very limited potential of technical improvements and shows that behavioural and collaborative endeavours promise dramatically higher improvements in eco-efficiency. This calls for a reconsideration of the focus of efforts to increase eco-efficiency for sustainable development.