The ratio of two quantities of the same kind and in the same units is a comparison by division of the measure of two quantities.
In other words ,the ratio of two quantities of the same kind is the relation between their measures and determines how many times one quantity is greater than or less than the other quantity.
The ratio of a to b is the fraction a/b, and is generally written as a:b.

• Example 1: The ratio of $25 to $50 is 25:50 or25/50 or 1:2
• Example 2: The ratio of 2m to 80 cm is 200:80 or 200/80 or 5:2
• Example 3: There is no ratio between $10 and 5 meter.

Since the ratio of two quantities of the same kind determines how many times one quantity contains other, is an abstract quantity. In other words, ratio has no unit or it is independent of the units used in the quantities compared.

For the ratio a:b, a and b are called terms of the ratio. The former a is called the first term or antecedent and the later b is known as the second term or consequent.