How much storage do I need - 16, 32 or 64Gb?

The items that can fill up your iPad quickly are the content.

• iTunes movies can be 1-3GB in size for SD depending on the length. If you prefer watching HD, they can be 3-5GB. If you want to take advantage of the Retina display to watch 1080p movies... you will need to watch out.
  
• iTunes TV shows can be a quarter to half the size of movies, but more than make up for it by the number of episodes typically available.
  
• If you get your movies and TV shows from somewhere other than iTunes, you're still looking at about 400MB an hour for SD and over 1GB  (sometimes way over) an hour for HD (high definition.)
  
• Music files are generally quite small but can add up as well, especially if you have lots and lots of albums you want to keep with you everywhere.
• Games can be big, and with the new iPad's 2048x1536 Retina display and Apple A5X processor, we might see even bigger ones with more textures and richer environments. Some games were already getting close to 1GB, will Retina iPad games be bigger?
  
  

Who should purchase 16GB? If you are just using email, surfing the net and reading iBooks and magazines, if you don't use a lot of apps, if you don't want to have a lot of movies and TV shows, or a huge amount of music, if you don't intend to keep very many 5 megapixel photos or 1080p video on your iPad, you'll probably be okay with 16GB.

Some people like to keep their iPads light and either stream or surf the web for content, and some people manage their photos and videos very well, transferring them to their computers regularly and reliably, or use iCloud or Dropbox.

If you keep your iPad lean, you can probably save yourself some cash and get by on 16GB.

Who should move up to 32GB? If the iPad is your primary device, if you play games on it and watch movies and TV shows on it, if you have a decent sized music collection you want to keep with you, and if you shoot an average amount of photos and videos, 32GB is probably your sweet spot.

Some people like to have one device that, while it doesn't do everything all the time, is capable enough to do most things most of the time. As long as there's some extra space to give extra time to managing apps and content, it's a great compromise.

If you store a fair but not overwhelming amount of data on your iPad, you are probably better off going for 32GB.  (The editor has a 32GB model.)

Who should go for the 64GB? If you're a power user who wants to keep as much as possible for as long as possible, if you have a large amount of apps and games, TV and movies, and a huge music collection you simply have to have with you all the time, or you shoot photos and video almost non stop and don't want to have to bother transferring it all the time... we'll, you've probably already ordered a 64GB iPad and cursed Apple for not giving you a 128GB option!

Some people really do want their iPad to do everything, all of the time, and never (or rarely) have to worry about running out of space. If you really feel like you need it, you probably didn't need me to tell you so, and you've already decided you're getting 64GB. 

What if you choose the wrong size?  Remember, in most places you have time to try out your new iPad and return it if you don't like it. Make sure, as soon as possible, you put your new iPad to realistic use. Load up all the apps and games you want with you, load up your movies and TV shows, go out and take some photos and shoot some video. Give it a complete and thorough workout and see.

If it feels like you got too much storage, say 64GB and you haven't even gone past 2GB, or if you got too little, say you're already at 15GB of 16GB, then take your iPad back and exchange it for one that better suits your needs.

If you come to this realisation too late, after the exchange period is over, remember you can buy additional iCloud storage, or look at other options like Dropbox which will let you keep your stuff available online and potentially free up some much needed space on your iPad.