Question: We've got some fraction information stored in the database, e.g. ¾ ½

Short of doing a search and replace, are there any inbuilt PHP functions that will automatically convert these to proper html entities?

Answer: 
You can use the [htmlentities() function](http://us3.php.net/htmlentities). This will replace all special characters with their HTML equivalent. It should do the job.
[htmlentities](http://de3.php.net/manual/en/function.htmlentities.php).

But you probably don't need to. Serve your page in an encoding that includes them (UTF-8, ISO-8859-1) and you can include those as literal, unescaped characters.