This study proposes a metric that builds upon the Lorenz curve to measure litter concentration on beaches. We apply the Gini coefficient and the Lorenz curve asymmetry coefficient (LAC) to quantify the Lorenz curve. We address not only the degree of litter concentration but also the causes of a certain degree of concentration in relation to the size of beaches defined by litter counts. We compiled the Gini coefficients along with the corresponding LACs based on a beach survey dataset that contains 10,262 records of litter counts for 1,803 distinct beaches in the UK from 2000 to 2016. We found that the degree of litter concentration varies by litter type, with plastic and pottery being the least and most concentrated respectively. A certain degree of litter concentration is due equally to the accumulation of litter from both small and large beaches regardless of the types of litter.