<ul style="text-align: justify;">
  {% for tag in site.tags | sort: 'key' %}
    <li style="display: inline-block;">
      <a href="/{{ tag | first | slugize }}">
         {{ tag | first }}
      </a>
    </li>
  {% endfor %}
</ul>

<ul style="text-align: justify;">
  {% for tag in site.tags | sort: 'key' %}
    <li style="
      display: inline-block;
      font-size: {{ tag | last | size | times: 30 | divided_by: site.tags.size | plus: 80 }}%;">
      <a
        href="/{{ tag | first | slugize }}"
        title="{{ tag | last | size }} {{ tag | last | size | times: 30 | divided_by: site.tags.size | plus: 80 }}%">
         {{ tag | first }}
      </a>
    </li>
  {% endfor %}
</ul>

Tag cloud displays tags in relative size
Tag cloud displays tags in relative size
