How to sing Twinkle, Twinkle, Little Star in your key
Twinkle, Twinkle, Little Star spans 9 semitones (C4 to A4 in its usual key), 42 notes. That's an octave or less, so it fits most voices once it's in the right key.
Words
Twinkle, twinkle, little star,
How I wonder what you are!
Up above the world so high,
Like a diamond in the sky.
Twinkle, twinkle, little star,
How I wonder what you are!
Finding your key
A song is in your key when its highest note sits at or just below the top of your comfortable range. Measure your range, then move the melody so its top note (A4 here) lands one or two semitones under your easy top. Singsteady does this for you and scores every note as you sing.
1806 words (Jane Taylor); 18th-century French tune. Melody and words are in the public domain. Notes transcribed from the score in Wikipedia, “Twinkle, Twinkle, Little Star” (score).