The `Reader` actress was the first celebrity to be "audited" by the UK Film Council, which looked to put a specific value on the country`s creative industries and chose the English star as the first example for her success abroad and public profile.
David Steele, the head of research and statistics at the UK Film Council, explained: "When an actor achieves international prominence, they have a general effect of boosting their country of origin that works its way through television appearances, advertising and celebrity news."
A friend said Kate - who won the Best Actress Oscar for `The Reader` this year - found it "both flattering and very funny".
The audit assessed salaries, profile and "box-office effect" on tourism and entertainment sales to find the figure, which has been nicknamed `the Winslet algorithm` and may now be used to work out the value of other famous faces, including `The Dark Knight` star Christian Bale and current James Bond Daniel Craig.
Kate, 34, is estimated to have earned £20 million from her movies since 1995, while the head designer of car manufacturer Jaguar admitted he had Kate`s curves in mind when designing the new XK model.
The `Revolutionary Road` star is Britain`s third-highest paid actor - earning £6 million for `Finding Neverland - with `Harry Potter` star Daniel Radcliffe and `Hugh Grant` earning £8.2 million and £7.5 million respectively for `Harry Potter and the Order of the Phoenix` and -Two Weeks Notice-.