How to sing Joy to the World in your key
Joy to the World spans 12 semitones (D4 to D5 in its usual key), 58 notes. That's an octave or less, so it fits most voices once it's in the right key.
Words
Joy to the world, the Lord is come!
Let earth receive her King;
Let every heart prepare Him room,
And heaven and nature sing,
And heaven and nature sing,
And heaven, and heaven, and nature sing.
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 (D5 here) lands one or two semitones under your easy top. Singsteady does this for you and scores every note as you sing.
1719 words (Isaac Watts); tune 1839 (Lowell Mason). Melody and words are in the public domain. Notes transcribed from the score in Wikipedia, “Joy to the World” (score after Mason, 1839).