noun, plural ra·tios.

- the relation between two similar magnitudes with respect to the number of times the first contains the second: the ratio of 5 to 2, written 5:2 or 5/2.
- proportional relation; rate: the ratio between acceptances and rejections.
- Finance. the relative value of gold and silver in a bimetallic currency system.

Latin.

- the final argument of kings (a resort to arms): motto engraved on the cannon of Louis XIV.

noun plural -tios

- a measure of the relative size of two classes expressible as a proportionthe ratio of boys to girls is 2 to 1
- maths a quotient of two numbers or quantitiesSee also proportion (def. 6)

1630s, “reason, rationale,” from Latin ratio “reckoning, numbering, calculation; business affair, procedure,” also “reason, reasoning, judgment, understanding,” from rat-, past participle stem of reri “to reckon, calculate,” also “think” (see reason (n.)). Mathematical sense “relationship between two numbers” is attested from 1650s.

n. pl. ra•tios

- Relation in degree or number between two similar things.
- The relation between two quantities expressed as the quotient of one divided by the other.

- A relationship between two quantities, normally expressed as the quotient of one divided by the other. For example, if a box contains six red marbles and four blue marbles, the ratio of red marbles to blue marbles is 6 to 4, also written 6:4. A ratio can also be expressed as a decimal or percentage.

An expression of the relative size of two numbers by showing one divided by the other.