Dimensionless quantity is also known as the quantity of dimension with one as a quantity which is not related to any physical dimension. It is a pure number with dimension 1. These dimensionless quantities are widely used in Maths and Physics. These quantities are obtained as products or ratios of quantities.
Following are the example of physical quantities that have units but are dimensionless:
|Atomic mass||AMU = 1.66054 x 10-27kg|