What does ratio mean?
A ratio expresses a comparison between two quantities, measurements, or groups. It can be represented in several ways: as a colon-separated form such as 3:2, as a fraction, or verbally as “three to two.” In finance, science, industry, and everyday discussion, ratios are used to compare rates, proportions, efficiencies, or relationships. A price-to-earnings ratio, for example, compares a company’s share price with its earnings per share, while an aspect ratio describes the relationship between the width and height of a screen or image. More broadly, “ratio” can refer to the general relationship or correspondence between people, groups, or things, although this use is less common than the quantitative sense. The term comes from Latin and is closely related to rational and ration, reflecting its long-standing connection with mathematical reason and comparison.
A comparison between two quantities, measurements, or amounts, usually expressed as the relationship of one to the other.
"The ratio of male to female applicants was nearly even."
A ratio is distinct from a rate, which commonly expresses a quantity per unit of time.
A broader relationship, proportion, or correspondence between people, groups, or things.
"The committee examined the ratio of teachers to pupils in rural schools."
The plural is formed by adding -s.
"The researchers compared the ratios of two different populations."
Ratios turn comparisons into a common language: they show not just how much there is, but how the parts relate.
Reviewed by Deb Chak, Editor. AI-assisted content curated by RJS Tech Solutions LLP.
Where does ratio come from?
The word comes from Latin ratio, meaning “reason” or “calculation,” and entered English in the late 16th or early 17th century in mathematical and rhetorical contexts. Latin ratio is related to ratus, “calculated, settled, or determined,” and is also the source of ration and rational. Its development reflects the idea of determining one quantity through comparison with another.
Related word forms
How ratio is actually used
In mathematics and everyday quantitative use, a ratio is commonly written with a colon, as in 3:2, or as a fraction, as in 3/2. The word is formal but broadly understood; in some contexts, a ratio may be confused with a rate, which usually includes a measurement per unit of time.
Easily confused with ratio
A ratio compares two quantities with one another, whereas a rate measures a quantity in relation to a particular unit of time or another basis.