Water has a density of 1 g/cm³ = 1,000 kg/m³ at 4°C. Objects denser than water sink; less dense objects float. Ice is slightly less dense (0.917 g/cm³) which is why it floats.
Q: How to calculate density?
Density = Mass ÷ Volume. Example: A 200g object with volume 100 cm³ has density = 200÷100 = 2 g/cm³. This is useful in material science, shipping, and chemistry.