These "line-height" classes are absolute in visual size. This means that regardless of whether your html tag is a <h1> – <h6>, <p>, etc... the line-height of these elements will be identical once the class is applied.
The quick brown fox
jumps over the lazy dog.
<p class="lh-1">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-2">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-3">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-4">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-5">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-6">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-7">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-8">Text</p>
The quick brown fox
jumps over the lazy dog.
<p class="lh-9">Text</p>