Decoupling environmental ‘bads’ from economic ‘goods’ is a key part of policies such as green growth and circular economy that see economic growth as desirable or necessary, and also see that current use of natural resources and its environmental impacts is unsustainable. We estimate what a ‘successful decoupling’ (2% annual GDP growth and a decline in resource use by 2050 to a level that could be sustainable and compatible with a maximum 2°C global warming) would mean in terms of its type, timeline and size. Compared to 2017, ‘successful’ decoupling has to result in 2.6 times more GDP out of every ton of material use, including in-use material stocks. There are no realistic scenarios for such an increase in resource productivity.