Is 750 mb of wifi a lot on an iPhone 4S?

[Lucy]

I'm on a new contract for my iPhone 4S and I've only just realised that my wifi is limited! I only have 750mb! Is this a lot? I'm always connected to wifi when I'm at home, even when I'm not using it. I only really use it for Facebook and Twitter which I check regularly throughout the day. I sometimes search the web to find out information. I very very rarely go on YouTube using wifi. Will my wifi get used up very quickly if I'm using it this often for these websites when I only have 750mb to use throughout the month?
It is definitely wifi! I have 250mb of mobile data (which is the 3G) and then 750mb of wifi! Wifi is not unlimited on my contract unfortunately! And I only just found that out.