How many litters capacity plastic container will be sufficient to float a body of 70 KG?

Since a normal human is quite close to the density of water, it does not require much added buoyancy to keep one afloat, to keep from drowning only the head need to be above water. I would estimate that a typical commercial life vest is not much more than 4 or 5 liters. One thing to consider is that a flood is much different than being in say, a swimming pool, moving water (perhaps rapidly) and debris also present hazards, so simply staying afloat is only part of the problem, but having a couple of empty plastic bottles (maybe 2 to 4 liters each) couldn't hurt and might be helpful.

If you go strictly by theory, then the density of the overall structure must be less than that of sea water ie the volume of water displaced by the body and container must exceed 70 kg.

ρ ~= 1 kg / liter

So 70 kg should occupy over 70 liters

volume of body + volume of container > 70 liters

According to the site below, a 70 kg human should occupy approximately 70 liters, so as long as the container can float on its own and is easy to hold onto, then it should work.

It should be mor than 70 l. Bat its shape should be designed to stable equilibrium, otherwise person that on it is rotates with the container by 180 degrees.

412