If you’ve not yet mastered all of the note names in the major scales, it can be challenging to remember which notes are the 3rd and 5th notes of any given scale.
A simpler approach is to learn two different intervals: a major 3rd and a minor 3rd. An interval is the distance between any two notes.
A major 3rd interval = 4 semitones.
A minor 3rd interval = 3 semitones.
All 4 chord types are different combinations of these two intervals:
Major chord = a major 3rd + a minor 3rd
Minor chord = a minor 3rd + a major 3rd
Augmented chord = a major 3rd + a major 3rd
Diminished chord = a minor 3rd + a minor 3rd
Let’s use an A as our root for the 4 chord types.
A Major chord = a major 3rd + a minor 3rd
Using the circle of notes, find the A and count the next 4 semitones moving clockwise. The note you end on is C#. So, C# is a major 3rd above the note A. So the first two notes of the A major chord are A and C#. Next, start at the C# in the circle of notes and count the next 3 semitones, again moving clockwise. You’ll find that a minor 3rd above C# is an E. So, the A major chord is A, C# and E as the 1st, 3rd, and 5th notes in the A major scale.
A minor chord is the opposite of a major chord. It has a minor 3rd at the bottom and the major 3rd above that. Again, starting on A using the circle of notes, three semitones (a minor 3rd) to the right of A is C. A major third (4 semitones) above the C is an E. So the A minor chord is spelled A,C and E.
An augmented chord is two Major 3rd intervals. We know from the major chord that C# is a major third above the A. What note is 4 semitones (a major 3rd) clockwise from C# in the circle of notes? E#.
So, the A augmented chord is spelled A, C# and E#.
The diminished chord is two minor third intervals. We know from the minor chord that C is a minor third above A. What note is a minor 3rd (3 semitones) clockwise from C? D# or Eb, which are e harmonic equivalents. So the A diminished chord is A, C and D#.
This works no matter what key you’re in, what the root of the chord is, etc.
Just using the circle of notes and two intervals (a major third and a minor third), you can make any of the 4 chord types starting on any note. For me, remembering those 3 things (the circle of notes, a major 3rd interval = 4 semitones, and a minor 3rd interval = 3 semitones) is much easier than memorizing the notes of the 11 possible major scales.
Just a different way to look at chord construction.
Let me know if this works for you!