In the sixties, American diet guru Ancel Keys popularised an index for measuring obesity by dividing a person’s weight by the square of their height. Since the late nineties we know this index by the abbreviation BMI – Body Mass Index. The isolation of our adipose tissue from the rest of the body, and its subsequent judgement of our health prospects, turned fat into an entity that was both familiar, yet foreign to us, defining fat as something “other”, rather than “of” us. If anything, fat became a product to consume or discard. In 2007 it was calculated that the global human population had accumulated 15 million metric tonnes of excess fat, but what does this mean? The BMI Pledge Calculator proposes an individual quantity of fat to be donated towards the growth of the FATBERG.