Density= Mass/Volume
To find the density of any object, you need to know the Mass (grams) of the object, and its Volume (measured in mL or cm³). Divide the mass by the volume in order to get an object’s Density.
Density of Water = 1g/cm³ at
20°C

How can you tell if something will float in water? The density of water = 1g/cm³ at 20°C.
Answer: Compare the density of the object in question to the density of water. If its density is less than water, it will float. For example, oak floats because its density is 0.7 g/cm³.
If the density of an object is greater than water, it will sink.

Will aluminum float
in water?
Density of Water = 1g/cm³
Density of aluminum = 2.7g/cm³
Answer = NO! Aluminum will sink in water.
Why? The density of aluminum is greater than the water it displaces, so it sinks.

Density = 2.7g/cm³ 
Will a chunk of
pine wood float?
Density of pine = 0.50g/cm³
Answer = YES!
Why? The density of the wood is less than the water it displaces, so it floats. 