 It's also National No Bra Day today. The bra was invented in France in the 1890s. Before that, women wore full corsets. The average American bra size, bet you didn't know this, maybe you do, is 36DD. That's a huge increase since the 80s and 90s. Before the 70s, there was no such thing as a sports bra. So women invented their own by hooking two jock straps together.