BBC One's coverage scored a high of 13.73m (54%) at 9pm as Bolt became the first man to successfully defend the men's 100m and 200m Olympic sprint titles.
However, the figures do not count those tuning in on BBC Olympics 1, big screens or in pubs.
Bolt's race - in which he beat compatriot Yohan Blake - was easily the most popular event of Day 13 of London 2012.
Meanwhile, the first ever Olympic women's boxing finals were witnessed by an average of 3.93m (36.7%) between 4pm and 7pm, climbing to a high of 5m (36.7%) in the last 15 minutes.
Olympics Breakfast (1.56m/40.1%) and Olympics Tonight (3.45m/27.9%) continued to pick up solid ratings.
BARB ratings data supplied by Attentional