..(But i have 4gb memory card..1gb full & my phone shows 3.7gb free memory in it
All discs in a computer or in memory cards will loose some space when you format the card. I am not in for geeky stuff but your card is just fine in this matter as I can see.
Just take a look on the disc(s) you have on your pc and you will find that some storage is vanished in reality.
Nokia 808 (Main device), Nokia 700 (Sport Phone/My Love :-) ) Nokia 701, Nokia E6 (Should have a follow-up from Nokia among with larger screen, NFC, Autofocus), Lumia 800 (Retired After 6 weeks), -Sugarsync-Funambol-Swype from Nokia betalabs-Sports Tracker-Nokia Internet Radio-Handy Safe-Skype-Bambuser-Screenshot app pro-fMobi-ComingNext-Manual TaskSwitcher-jagiTimer-Easy StopWatch-Boldbeast-Equalizer-Financial Calculator-WiMP Music-YTasks-Davi-Thumbnail Folders-BizCalendar-Tiny7-Situations-nn reeder-Sport Timer-CameraLover-CameraPro-GrabRadio-LiveScore-Poddi-Gravity-SkyFilesPro