Object relative density = D wrt water.
let mass of object = M. let its volume = V. Its density = d.
density of water = d_w. then D = d / d_w and M = d V
1) if D > 1 then the body is denser than water. Then it will sink to the bottom of the water container.
2) if D = 1, then the body is as denser as water. It will float on water surface. The upper part of the body will be just at the same level as water surface. The entire body will be under water.
3) if D < 1. then the body will float on water. Let some part (volume V1) be immersed in water. As per Archimedes law
mass of the body = mass of water displaced.
D* d_w * V = V1 * d_w
V1 = volume immersed = D * V = d / d_w * V = M / d_w
If we take the CGS system, d_w = 1 gm/cc
Volume immersed = Mass in grams.
If we take the MKS system, d_w = 1000 kg/m^3
Volume immersed = (mass in kg /1000 ) m^3