Quantity is a generic term used when referring to the measurement (count, amount) of a scalar, vector, number of items or to some other way of denominating the value of a collection or group of items.

It is usually represented as a number (numeric value) of units together with the type of those units (if required) and a referent defining the nature of the collection. Both parts are required.

Examples are

• one apple, two apples, three apples, where the number is an integer so does not require a type
• 1.76 litres (liters) of milk
• 500 people

A number by itself is not a quantity, nor is a simple measurement. Where the unit count is one then the indefinite article may be used (for example, a car) and similar alternatives exist for other particular counts (for example, a brace of pheasant, a dozen eggs).

Quantification in its very simplest sense can be found in statements such as "A is greater than B". In the example cited, an expression is made that A has a greater quantity of something (such as volume or charisma) than B; and that if A and B were placed in an ordered set, then A would come after B if the order is arranged on an increasing (rather than decreasing) scale.

In linguistics, quantity refers to a contrast of the physical duration, see length (phonetics). With consonants, the longer quantity is called gemination, and the term long vowel is used for vowels. English does not contrast anything by quantity alone, but Finnish has two (long and short) and Estonian three (over-long, long and short) levels of quantity.