How to harmonize a melody on guitar using 3rds and 6ths

One way to enhance your melodies and improvisations on guitar is by harmonizing them—adding notes above or below the melody to create depth and expression.

In this lesson, you’ll learn how to harmonize melodies using two powerful intervals: 3rds and 6ths. These intervals add richness and movement, making your lines sound fuller and more expressive.

Before diving in, I recommend getting familiar yourself with the 5 Major scale shapes, as they provide the foundation for finding harmony notes across the fretboard. Now, let’s explore how to apply 3rds and 6ths to your melodies!

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Identify which scale to use

Melodies are built from scales, so the first step in harmonizing is knowing which scale the melody comes from. The Major scale is a great starting point, as many melodies are derived from it.

To understand the Major scale, it’s important to learn its formula—the pattern of whole and half steps that create its structure. Here’s how the Major scale is built:

For example, here is one way to play the C Major scale in one position:

Once you know the formula that makes up a Major scale, you can also apply this to start on any given note to find the notes of other Major scales.

How to harmonize a melody

Once you’ve identified the scale, you can start harmonizing by adding notes from that scale. One of the most common ways to do this is by using 3rds—playing a note and then adding the third note above it in the scale.

For example, in C Major, harmonizing in 3rds would look like this:

• C → E

• D → F

• E → G

• F → A, and so on.

To find a 3rd above any note, simply skip the next note in the scale and play the one after it.

Below, you’ll see the Major scale with 3rds added to each note, along with a guitar-friendly way to play them. Pay attention to the finger numbers above the notes to help with comfortable fretting-hand positioning.

C Major scale harmonized in 3rds

C Major scale harmonized in 6ths

For 6ths, count six notes up from the melody note within the scale. Another way to think about it is that 6ths are inverted 3rds—essentially, a 3rd interval shifted an octave lower.

For example, in C Major:

• C → A

• D → B

• E → C

• F → D, and so on.

6ths create a more open and melodic harmony, making them a great choice for adding warmth and movement to your melodies. Try the example of 6ths on guitar below.

Melody example in C

Before we dive into harmonizing, let’s start with a short melody in the key of C Major that we’ll use for the following examples.

Here is a backing track of what this melody sounds like:

Now try this example of the same melody now with the interval of a third above the notes.

3rds above the melody

3rds below the melody

You can also try thirds below the notes by skipping the previous note of the scale.

Here is what this would like:

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How to harmonize a melody in 6ths

Now, let’s harmonize the melody in 6ths which create a fuller sound to the melody line.

6ths above the melody

6ths below the melody

Harmonization tips to create variations in music

Harmonizing notes is also a great tool to create variations in music. You might want to play a single line the first time around and then harmonize the melody to create a variation.

Let’s see some examples below.

Variation 1

In this example, we’ll start measures 1 and 2 with the original melody. Then we’ll use 6ths above the melody on measure 3 and the 3rds above the melody at the end of measure 4 to provide some contrast when repeating the phrase.

Breaking up intervals (Variation 2)

Another nice compositional tool you can add to your playing is to break up up the intervals into different rhythms to create a nice musical pattern.

Here is an example where we can split up some intervals of 6ths in 8th notes. I only add these rhythm variations to the notes that were originally half notes since we have some space to fill in there.

You can use these intervals to enhance specific phrases or sections of a piece. With practice, you’ll develop a better ear for when to add harmonies in a way that complements the melody tastefully.

Melody harmonization exercises

To practice harmonizing melodies, start by choosing a scale and making sure you can play and name each note in order. Learning key signatures will also help you quickly identify the notes in any scale.

Practicing 3rds:

1. Play a scale and name the note that is a 3rd above each scale note.

2. Do the same for a 3rd below each note.

3. Begin practicing on the 1st and 2nd strings, as melodies often sit in a higher range.

4. Once comfortable, try harmonizing on the 2nd and 3rd strings, then other string pairs.

Practicing 6ths:

1. Apply the same process using 6ths above each note.

2. Practice harmonizing both ascending and descending to develop fluency.

Bonus Tip:

Understanding how harmonized notes fit within a chord progression can make harmonization easier. Instead of thinking of a different scale for each chord, use one scale to harmonize notes over a series of related chords.

Wrapping up

To recap, harmonizing a melody on guitar starts with understanding the key and scale you’re using. I highly recommend mastering your 5 Major scale shapes so you can easily add different intervals above or below melody notes.

The most commonly used intervals for harmonization are 3rds and 6ths, which you’ll frequently hear in songs. These intervals sound great and can be applied to melodies you enjoy—or even ones you create yourself!

Once you’re comfortable with 3rds and 6ths, you can explore other intervals like 4ths, 5ths, or 7ths, which we go over in on how to practices scales.

Have fun adding harmonies to melodies you already know—or using them to compose your own music!

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