Solid line = floor (spellings that unambiguously belong to the group). Shaded band up to the dashed edge = ceiling (the most it could reach if every ambiguous spelling counted here).
Brian is now well below its former popularity. All-time it's been given to 1,592,540 U.S. babies, the 357th most common name by sound today, peaking at 44,226 in 1972, with 2,008 in 2025.
By sound, Brian also includes the spellings Bryan, Bryon, Brain, Brien.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).