Definition
Quantity
A quantity is an amount you can count or measure, often written with a number and a unit.
What it means
Quantity answers “how many?” or “how much?” A number gives the value. When something is measured, a unit tells what kind of measure it is. So 12 can name a count, while 12 cm names a length.
Remember it
Ask two quick questions: how many, or how much? The answer is a quantity.
Example
A box holds 9 crayons and has a mass of 240 g. “9 crayons” is a counted quantity. “240 g” is a measured quantity: 240 is the value and g is the unit.
Watch for
A property such as red or wooden is not a quantity by itself. It becomes part of a quantity when it is counted or measured, as in 5 red blocks.
Common mix-up
A number and a quantity are related but not identical: 12 is a number, while 12 litres is a quantity with a unit.
Exact meaning
A quantity is an amount, count, or measurable magnitude. A measured quantity combines a numerical value with a unit, such as 8 cm; a counted quantity can be named by a number of objects, such as 8 shells.