This is the most useful reference for music! I wrote out exactly the structure of almost all chords in semitones. Once you know how many semitones are in between each note in a chord, you can figure out any chord!
For example, D major chord starts on D, then will have four semitones between the first two notes (F#), and three semitones between the last two notes (A). So the notes in a D major chord are D, F#, A.
Go ahead, count on your keyboard to see! The visualization here are for chords in C.
This is a must have for your music space! I have this hanged on my wall!