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).
Louise was more common in the past and has since settled at a lower, steady level. All-time it's been given to 338,662 U.S. babies, the 1,027th most common name by sound today, peaking at 9,226 in 1920, with 579 in 2025.
Louise has no common alternate spellings by sound. Spellings sometimes heard the same way: Luiz.