How to improve my calculation and guess my opponents move I am a 1100 rated player.In rapid and blitz games I beated 1600 players this proves that my intution is good but at classical matches I can't even handle a 1300 player.I am a positional player as I just need a moderate advantage .But I am weak in long term calculation as I can't judge my opponent's move so kindly tell measures improve my calculation
You could make your question more specific, giving examples of when and what type of moves you fail to take into account. Anyway, I am 2050 and suffer from the same, so, it is a relevant concern for players of all levels! Start with distinguishing forcing moves, from non-forcing ones. Basically, unless you've given a check, your opponent can, in theory, play any move they wish. Thus, look for as many possibilities as you can afford the time for. My own problem: I tend to fool myself into believing that my opponent and I together are trying to produce a stunning, beautiful game! As if he/she will not ruin my beautiful strategy I have in mind, and they will help me carry it out!! "I attack this pawn and of course they will defend it..." And then I got the shocking response that sends chills down my spine, waking me up from my dream :))

Do not ASSUME that by default your opponent will respond in the way you think they should/must. Try to look for all possibilities on their behalf. Look for the strongest they can play.