When quantities have the same **relative** size. In other words they have the same ratio.

Example: A rope's length and weight are in proportion. When 20m of rope weighs 1kg, then:

• 40m of that rope weighs 2kg

• 200m of that rope weighs 10kg

etc.

Another example: The lengths of these two shapes are proportional: every matching side on the larger shapes is twice as large as on the smaller shape.