ChartReign — Every chart has a #1. Only one artist wears the crown.

Each week an artist's share is the weighted mean of their Power Share across Billboard Hot 100 ×1 and UK Singles Chart ×0.45 (weights ∝ √population, US = 1). The divisor is every chart's weight, so a number one is worth the same share in any era — and a week before every chart exists, or after one's data ends, sums to less than 100.

UK Singles Chart data runs to Sep 18, 2026; later weeks combine the Billboard Hot 100 only, so their shares — and the most recent years' Era Power — are lower than a full week's would be.