Questions and answers

What is the difference between density and specific gravity?

Measuring or comparing

Density and specific gravity are both used to describe mass and can be used to compare substances. However, they are not identical measures. 

  • Density is defined as mass per unit volume. It has the SI unit kg m-3 or Kg/m-3 and is an absolute quantity.
  • Specific gravity is the ratio of a material's density with that of water at 4 °C (where it is most dense and is taken to have the value 999.974 kg·m-3).  It is therefore a relative quantity with no units.

The words ‘taken to have the value’ are important here, as the value of maximum density cannot be known exactly (nor, for that matter, can the temperature of 4 °C be realised exactly).

DigitalTime and frequencyEnvironment

Measuring gravitation with Optical Atomic Clocks


Bushy House Open Day

22 Sep

10:00am to 5:00pm


Find Bushy House

Work with us

Our research and measurement solutions support innovation and product development. We work with companies to deliver business advantage and commercial success.
Contact our Customer Services team on +44 20 8943 7070