This essay introduces a new type of measure of social welfare, where populations are evaluated by their resemblance to an optimum population, which is an (in principle) possible population with the highest degree of social welfare, relative to some circumstances. Here, it is argued to be the largest possible population where everyone fares maximally well. The new measure is responsive to quality of welfare, equality of welfare and the number of people. It satisfies dominance and negative monotonicity, and it avoids both the repugnant conclusion and a reverse repugnant conclusion for comparisons relative to our future on earth.