Plural of Formula

The Quick Answer

The plural of formula is formulas or formulae.

The Plural of Formula

The plural of formula is formulas or formulae.

Formulas are applied to provide a mathematical solution for real world problems.
Formulae are used to express relationships between various quantities.

The noun formula has a Latin root, which is the derivation of the plural formulae. Through common usage, formulas (which adheres to the standard rules for forming plurals) is also now acceptable.

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The Standard Rules for Forming the Plurals

The table below shows the standard rules for forming the plurals of nouns in English.

Type	Example of Type	Forming the Plural	Plural
Most Nouns	formula scythe	add s	formulas scythes
Noun Ending s, sh, ch, x or z	box dress	add es	boxes dresses
Nouns ending [consonant] o	hero zero tomato	add either s or es (There are no rules for this - you have to know.)	heroes zeros tomatoes
Nouns ending [vowel] o	patio ratio	add s	patios ratios
Nouns ending [consonant] y	story penny	change the y to an i and add es	stories pennies
Nouns ending [vowel] y	donkey chimney	add s	donkeys chimneys
Nouns ending f or fe	dwarf hoof	ves and/or s (There are no rules - you have to know.)	dwarfs hooves or hoofs
Exceptions	man louse	some nouns undergo a vowel or letters change	men lice
More exceptions	salmon sheep	some nouns do not change at all	salmon sheep
Foreign rulings	formula medium	some nouns adopt foreign rulings	formulae media

Why Is There Confusion over the Plural of Formula?

Confusion arises over the plural of formula because its original plural form (formulae) derives from Latin, and native English speakers are drawn to formulas, which adheres to the standard ruling for forming plurals.

Both formulae and formulas are acceptable, but formulas is the more common plural and the safest option. (See the evidence in Google's Ngram Viewer.)

Another Interactive Exercise

Here are three randomly selected questions from another exercise on plurals, which can be edited, printed to create an exercise worksheet, or sent via email to friends or students.

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