There is an easy way to do this if you use a very neat piece of software called ClipboardFusion Pro, to be found at binaryfortress.com. It only costs $19 for the full version, but there is even a free version.
As the name suggests, it monitors the clipboard, but amongst the many things it can do is run a macro when a hotkey selection is pressed (I use CTRL ALT C). I have configured a macro so that a dialogue box pops up which shows number of keywords and number of characters in selected text when the hotkey is pressed. When not in use, it just sits unobtrusively on the taskbar (Windows).
I have attached a screenshot. In this case, it is counting the number of keywords. I could equally select the text in the Desription/Caption field and it would show the number of characters used in the caption. As you can see, it reports number of words, number of chararacters with spaces, number of characters excluding spaces, number of keywords and number of words (if you have multi-word keywords) - you can easily configure the macro to show whatever information you want, and cut out any that is not relevant for you to see.
Also attached is the code you need for the macro to produce this dialogue box. Copy and paste it into the macro editor and it should just work. It is very easy to do, even for me with no knowledge of programming.
This is only one use. You can store keywords, the clipboard history etc. - its uses are (relatively speaking) endless. It is a really useful piece of low impact software wittout unnecessary bloat.
Hope this helps.
Graham