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).
Kira is now well below its former popularity. All-time it's been given to 151,901 U.S. babies, the 435th most common name by sound today, peaking at 7,788 in 2006, with 1,690 in 2025.
By sound, Kira also includes the spellings Ciara, Keira, Kiera, Kierra, Keara. Spellings sometimes heard the same way: Kyra, Kera.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).