Using the two tables above, you will be able to determine the notes that make up just about any type of chord and in any key.

In Table 1, the notes for each key and their accompanying numbers have been entered. For example, for the key of “C”, the notes are C, D, E, F, G, etc and they are numbered as 1, 2, 3, 4, 5, etc.
Table 2 has the note numbers for each type of chord.
To start, let’s see how a major chord is constructed.
Looking at Table 2, we see that the notes for a major chord are 1, 3 and 5.
If we wanted to know the notes of a C major chord, we would go to Table 1 and see that for the key of C, the 1, 3 and 5 notes are C, E and G.
In other words, the notes for a C major chord are C, E and G. (Incidentally, a C major chord is almost always referred to as a C chord).
From Table 1, we see that a G chord is made up of the notes G, B and D and a C♯ chord has the notes C♯, E♯ and G♯. We could list the notes for any major chord in any key, so instead let’s investigate a different type of chord.
We see from Table 2 that a sixth chord consists of the notes 1, 3, 5 and 6. Using Table 1, we see that a B♭6 chord is made up of the notes B♭, D, F and G.

Now is the time to explain “Dominant 7th” and “Major 7th”.
When the notes of a key are numbered, the note that gets the number “7” is called the Major 7th note and the flat 7th gets designated as the dominant seventh.
For the key of C, the major 7th note is B and the dominant 7th note is B♭.
Looking at Table 2, a Major 7th chord has the notes 1, 3, 5 and 7 and a seventh chord’s notes are 1, 3, 5 and ♭7.
From Table 1, we see a C Major 7th chord has the notes C, E, G and B whereas a C7 chord consists of the notes C, E, G and B♭.
The C7 chord is not a C major 7 chord and actually is a C dominant 7th chord, a term almost no one uses and so it is generally referred to as just a C7 chord.
It is important that you know the difference between these two terms.

If you just want to know the notes or note numbers of a chord, simply go to this calculator:

Chord Calculator