The plural of nouns in English
1. Regular Plural Forms
1.1. How to form the plural
We form the plural by adding -s to the singular of the noun.
Singular
Plural
a car
two cars
a cassette
two cassettes
a lamp
two lamps
a hat
two hats
a cup
two cups
1.2. Nouns ending in sibilants
Add -es. Add -s if the noun ends in one -e.
Singular
Plural
a box
two boxes
Singular
Plural
a sandwich
two sandwiches
a suitcase
two suitcases
a rose
two roses
a garage
two garages
1.3. Nouns ending in -y
1.3.1. y after consonant
Change -y to -i, then add -es.
Singular
Plural
a city
two cities
a lady
two ladies
There are two forms of the plural of the word penny:

pennies → You refer to the single coins.

pence →You refer to the price (how much sth. is).
1.3.2. y after vowel
Add -s after a vowel.
Singular
Plural
a boy
two boys
a day
two days
1.4. Nouns ending in -f or -fe
1.4.1. Add -s
Singular
Plural
a roof
two roofs
a cliff
two cliffs
a sheriff
two sheriffs
1.4.2. Substitute with -ves
Singular
Plural
Singular
Plural
a thief
two thieves
a wife
two wives
a shelf
two shelves
Both forms are possible with the following nous:

scarf → scarfs/scarves

hoof → hoofs/hooves
Add -s for words ending in -ff.
1.5. Nouns ending in -o
1.5.1. Add -s
Singular
Plural
a disco
two discos
a piano
two pianos
a photo
two photos
1.5.2. Add -s
Singular
Plural
a tomato
two tomatoes
a potato
two potatoes
a hero
two heroes
Both forms are possible with the following nous:

buffalo → buffalos/buffaloes

mosquito → mosquitos/mosquitoes

tornado → tornados/tornadoes
2. Irregular Plural Forms
Singular
Plural
a man
two men
a woman
two women
a child
two children
a mouse
two mice
a tooth
two teeth
a goose
two geese
a foot
two feet
an ox
two oxen