That's somewhat right. Measured, her figure is 10.68", which equals 5' 3" when scale up. BUT this is still undersized because Scarlet is supposedly 5' 3" barefoot, and Black Widow is sporting some massive heals and her figure is still no taller than 5' 3".
Meanwhile, Chris Evans is 6 foot in reality, but they've scaled his figure up to nearly 13", which equals just under 6' 5".
So they've essentially scaled Captain America up to his comic book proportions, and scaled Black Widow down to less than even Scarlett's barefoot height, and you wind up with this wonky disparity in scale. Along with that, Black Widows limbs and features are also dwarfed by Cap and Tony (I mean you could fit three of her feet in Cap's boot alone). So it looks like she's 1/7 scale, and Cap is 1/5 scale.
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