In a new tutorial today from PHPMaster.com, they show you how to combine Javascript and a PHP feature to track the progress of an upload to your web application.

A problem that has plagued web developers for years is how to add real-time information to their applications, such as a progress bar for file uploads. [...] JavaScript can access a file’s name, type, and even the width and height of a local image, but it wasn’t until HTML5 that it could access a file’s size. [...] In this article I’ll show you how [the session.upload_progress] feature can be used to create a simple upload progress bar without any external libraries or browser dependencies.

The tutorial provides all the steps you'll need to get it working - defining the form with the extra required field, styling it and plugging the Javascript in to call a small script to get the progress of the upload. It returns the difference between the content-length of the file and the current size (as a percentage of 100).