Deprecated in HTML5. Do not use.

<big> HTML Tag

Element of
Fonts and Web Typography
What does <big> HTML Tag do?
The <big> element was used to cause the selected text to appear one size larger than the surrounding text. This purely presentational tag was removed from HTML5 and should not be used. Instead, use CSS to control font size.
Display
inline
Usage
textual

Code Example

Big text is <big>bigger</big> than regular text.
Big text is bigger than regular text.

It works, but don’t use it.

The <big> element is still supported in most browsers, but it is no longer a part of the HTML5 specification. That means that it is not valid, and it may not continue to be supported in web browsers. If you need text to be larger, use CSS and the em sizing unit (ems are relative to their surrounding text).

.big {  font-size: 1.3em; } 
Spans with class of "big" are <span class="big">bigger</span> than the surrounding text. 
#big { font-size: 1.3em; } Spans with class of “big” are bigger than the surrounding text.

Usually, even this is a bad idea. While it is valid HTML, there are very few instances where a span of larger-than-normal text, without any semantic motivation, is a good idea. If you find yourself doing something like class="big", ask yourself whether a headline tag (<h1>, <h2>, <h3>, etc.) or an emphasis tag (<em>, <strong>) would be more appropriate.

You can still use the <small> tag

The <big> element was deprecated, but the <small> element is still available in HTML5. This seems like an inconsistency (and it might be), but there are potentially legitimate uses for the <small> element within normal text. One example is subtitles.

<!-- This doesn't really make sense -->  <h1>The Title of the Page</h1> <h2>The Subtitle of the Page</h2>  <!-- Better idea -->  <h1>The Title of the Page <br> <small>The Subtitle of the Page</small></h1> 

The first example (using <h1> and <h2>) doesn’t make any sense because headlines elements are supposed to work in a sectioned hierarchy. The <h2> element should only refer to the content immediately following it, not to the whole document. For more information, see our documentation on the <small> element.