Q: How to know my ipad is 4...y it shows only 13.6 gb in usage when i check in settings....my ipad is 16gb

If it has the Lightning port, it is an iPad 4. iPad 3rd gen and all below came with the 30-pin connector. If you want, post the model number and we will verify what it is exactly.

Identify your iPad:

http://support.apple.com/kb/HT5452

Identifying iPad Models

http://support.apple.com/kb/HT5452

Have you Googled that part number? Multiple sources state that it's:

Apple iPad Retina Display Wi-Fi Cellular MD522HN/A (Black)

They also probably will NOT state that it's a 4th gen simply because Apple doesn't call it by that name. If it has a Lightning port, it's a 4th Gen.

The SIM tray is on the right-hand side looking at the iPad's screen. If you're looking at the back, it will of course be on the left-hand side.

Enter your model number here: Model Identifier Utility

The model number, beginning with "A," is printed on the back of the iPad, towards to bottom.

New ipad with Retina display MD522HN/A http://store.apple.com/us/ipad/compare

The model number he posted (MD522HN/A) shows on Indian websites if Googled but nowhere on Apple's website, not even the Indian website (at least as far as I can find). I also can't find/see how the SIM card tray would also be on the opposite side (left side) of the iPad as the OP states. Searching for that model number from Apple's website turns up no results either.

SergZak wrote:

 

The model number he posted (MD522HN/A) shows [...] nowhere on Apple's website

Right, that's why I wanted them to look for the printed model number, i.e. A1460.