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).
Erica is now well below its former popularity. All-time it's been given to 382,315 U.S. babies, the 1,149th most common name by sound today, peaking at 14,330 in 1986, with 435 in 2025.
By sound, Erica also includes the spellings Erika, Ericka.
Source: U.S. Social Security Administration, “National data” baby-names files (1880–2025).