h1 size change in html code example

Example 1: make text bigger html5

p {
  font-size: 15px;
}

p {
  font-size: large;
}

p {
  font-size: 150%;
}

Example 2: html h1 size

h1  =>    32px    (2em)
h2  =>    24px  (1.5em)
h3  =>  20.8px  (1.3em)
h4  =>    16px    (1em)
h5  =>  12.8px  (0.8em)
h6  =>  11.2px  (0.7em)