In total, three women broke through the US$20 million barrier this year, down from four a year earlier.
Confirmation of Stone's place at the top of the list comes shortly after the flame-haired star spoke out about the gender pay gap in Hollywood.
Stone said she hopes she can one day use her voice to help stamp out sexism for good.
She explained: "There is so much power to our voices, and we need to speak out. That's something that I struggled with in the past, but it's very hard not to feel galvanized right now, politically or consciously.
"Nobody is going down without a fight - for love and humanity and equality and coming together. It's so inspiring to see marches and beautiful writing and creative work.
"There's so much power and a grace coming out of so many people who have so much to lose, and the human spirit is incredible."
And Stone believes the "fight" for equality will ultimately prove to be worthwhile.
She said: "[Equality is] worth a fight every day. And I want to learn how to fight better."
- Bang! Showbiz