This usually depends on the size and number of images included in your website. The actual html of the web pages is an insignificant amount. Sites that require a very large number of images or other multimedia do require far more disk space than those sites that provide a quick loading text based website with a few images and buttons. As an example, the entire www.redrook.com web site itself only uses about 100MB of disk space!
Even the most basic of the Red Rook Web Hosting Packages, offering 50Mb of web disk space is more than enough for most web sites. 1GB of disk space as offered in the Business Hosting Package is far more than 99% of website owners / webmasters will ever require.