Men's and women's clothing use entirely separate sizing systems, and there's no single formula that covers all of them. Each category — shirts, jeans, shoes — converts on its own logic. Here's the short version of each, with a full guide for every one, plus a free tool that does the math for you.
Open the size converter →Shoes: the cleanest one — women's US size = men's + 1.5. A men's 8 is a women's 9.5.
Shirts & tops: by chest measurement, a men's size is about one letter above the women's equivalent (men's M ≈ women's L). Size up one more letter for the loose men's-cut fit.
Jeans: don't match the numbers — match the waist in inches. Men's jeans use real waist inches; women's use a smaller "vanity" number. A men's 32 waist ≈ a women's 10.
Only for shoes (add 1.5). Clothing has no universal formula because the garments are cut differently and women's sizes aren't tied to a measurement.
Work from a body measurement — chest, waist, or foot length — and match it to the target size chart, rather than trusting the size label alone.