What is the formula for calculating tide of sea water(water level at that time)?

Answer 1

Norfolk Broads real-time Tide Calculator
actual tide state at 02:48 (BST) on Thursday 07 September 2006

This Tide clock calculates low water at Gorleston Bar plus 1 hour to estimate LW at Yarmouth Yacht Station. Standard Broads deviations are then applied to calculate the heights at the other locations. The intermediate heights are based on 7 hours of Ebb and 5 hours of Flood, with the 'rule of twelfths' for each applied to give a graphical display of the approximate height at any time.
The clock initially displays in realtime. If you wish to see Tide states for the Broads for any date between 2003 and 2009, click the button to select your desired new date and time. The (24 hour) clock automatically corrects for scheduled BST/GMT up to the year end of 2007, from then onwards the times are GMT only.

http://www.shorebase.co.uk/broads/tides/broadstides.asp

Answer 2

there is no formula

tide levels are very complex and they are different for every coast and for every piece of coast

there are estimates based on history, moon position, etc but other things affect tide levels including storms etc