It’s a pretty heavy mix, many of the most popular rounds are also referenced by their metric size but they’re not usually ‘useful’ sizes in either standard or metric.

For example:

• .22 LR = .223in = 5.56 NATO
• 9mm = .357 mag
• .40 S&W = 10mm Auto
• .308 = 7.62mm
• .44 = no common metric eq.
• .45 = no common metric eq.
• .50 = 12.7mm