In this post, we will discuss on density and relative density physics of a substance. We will also look into their differences. So let’s start.

## What is the difference between density and relative density?

**Density** is the mass per unit volume. So if we divide the mass of a substance with its volume then we get the density of that substance. The unit of density in SI is Kg/meter^{3}.

The **relative density **or specific gravity of a substance is the ratio of its own density and the density of water. It’s a comparative parameter calculated with respect to water’s density. It’s a ratio of two densities and a number only without any unit.

### What is the unit of density in SI?

The unit of density in SI is Kg/meter^{3}.

### What is the unit of density in CGS?

The unit of density in SI is gm/centimeter^{3}.

## What is the density of ice in SI?

The **density of ice** is 916 kg/meter^{3 }in SI. This means if we take a slab of ice of unit volume (length=1 meter, breadth = 1 meter and height = 1 meter), and measure its mass then its mass will be 916 kg.

## What is the density of water in SI?

The **density of water** is 1000 kg/m^{3 } in SI. This means water of 1 cubic meter volume has a mass of 1000 kg.

Now we will discuss about Relative density or specific gravity.

## What is **Relative Density? **

The Relative density or specific gravity of a substance is defined as the ratio of its own density and the density of water.

It’s a number only without any unit.

### What is the **relative density of water**?

**The relative density of water** is certainly 1.

[Relative density of water = density of water/density of water = 1]

### What is the **relative density of ice**?

R**elative density of ice** = density of ice / density of water = 916/1000 = 0.916

### How does an ice cube float in water?

A substance with relative density more than 1 will sink in water and a substance with that value less than 1 will float in water.

The relative density of ice is only 0.916. So we can say an ice cube will float in water.

### What is the cgs unit of relative density?

It’s a number only without any unit.

### What is the SI unit of relative density?

It’s a number only without any unit.

## Why is the density of water used as the reference to measure relative density?

**We calculate relative density with respect to water**. Why? Generally, the density of water at 4 °C (the temperature at which the density of water reaches its maximum value) is used as the reference to measure relative density.

In SI units, the density of water is approximately **1000 kg/m ^{3}** and in CGS units it’s

**1 g/cm**which makes

^{3}**relative density calculations pretty convenient**.

The density of the material only needs to be divided by 1000 or 1, depending on the units.

## Relative density Examples

Here are some samples of relative density.**Water: 1Iron: 7.87Table Salt: 2.17Mercury:13.56**

Suggested Study: Mole vs Molecule