"I think I've always sort of been on the more boyish spectrum of girls. For example, I've never been chosen as 'one of the top-five hottest actresses in a bikini.' And honestly, it's a godsend," Roberts told the magazine.
"When I was younger, I'd think, 'Oh, I'm the prettiest one. It's not Halle Berry. It's not!' But it is, you know?"
Roberts went on to say over the years she's become more and more conscious of what she wears and what she looks like, adding that before "a friend could call me at 3 in the afternoon and say, 'I have a premiere tonight. Will you come?' And I'd just take a shower and go."
"I wore a lot of vintage then. I had a navy military jacket and striped leggings I wore all the time," she explained. "Those were the fun old days. People were less judgmental, less searing in their assessment of what you dare wear to the drugstore."
But now the Oscar-winner has friend and stylist Elizabeth Stewart and her kids -- twins Hazel and Phinneas, 9, and Henry, 7 -- to help her be on point for all her red carpet looks.
"Often I'll let the kids look at my outfit choices and say, 'What do you like better -- this or this?' I just try to not take it so seriously," she shared. "And it can be stressful on the red carpet So it doesn't matter how much you dress up or bejewel yourself, you've still got to feel like you."
The September issue of InStyle, which also commemorates the magazine's 20th anniversary, will be released on August 15.