Mar 06, 2020 · A ncentrated load of 90,000 lbs in one square inch, or even a square foot, is much different than a distributed 90,000 lb load over 1000 square feet. Similarly, how do you calculate water load on a slab? Dead Load: Self weight of the slab = Mass / Weight of the slab i.e. Density *Area. As we know that density of Reinforced ncrete is 25 KN/m3.