Looking for a plugin to calculate square footage

I’m hoping to find a calculator that I can add to my site for determining the square footage of a room(s) by entering the dimensions. For example someone would enter the measurement of length of the room in one box and the width in another and it would output the square feet (or multiply the 2 numbers).

Ideally I’d hope to find one that has 3-10 boxes to do multiple rooms, but a single room one would work. I don’t need it to determine the cost per square foot. Just the square footage.
This one is very nice and I’d be willing to purchase something this detailed
http://www.saybuild.com/sf/calc_footage.html

But I’d be ok with a simpler one like this;
http://www.had2know.com/househome/square-footage-calculator.html

I have searched through plugins, searched for themes on google, searched for code to add etc and I can’t seem to find what I need. I did find one but it had bad reviews a couple of which mentioned malware, it not being updated in a long time etc.

I’d greatly appreciate it if someone could either share the code for this, or a plugin that they know of. I know this is probably super simple stuff so please forgive me I am pretty new to doing work on my website. Thanks