iExplorer will display the size of any file in the Size column whenever you are looking at a file system view of your iPhone or iPad like in the Media and Apps sections (and Root with Jailbreak). If you want to also view the size of an entire folder, then just make sure you are using version 3.3.1 or later and right-click on any folder and choose "Scan Contents" (PC) or "Update Size" (Mac) which will display the size of that folder in the Size column.
If you'd like to view the folder size for several folders at once, then just select several folders while holding Command (Mac) or Control (PC) before right-clicking.
This can be extremely helpful if you are trying to locate large files on your device that are eating up your available storage without having to open each folder and look at the individual file sizes. For example, if the "Other" data on your iPhone or iPad is getting to be over 1 GB, and you aren't sure why, displaying the folder sizes will save you time searching through every subfolder. If you are experiencing the large "Other" data issue, please click on the article below:
How to find and reduce "Other" data.