If you are unsure whether to write sisters, sister’s, or sisters’, the answer depends on what you mean. These forms are not interchangeable: sisters is the plural of sister, sister’s is usually the singular possessive form, and sisters’ is the plural possessive form.
For example, I have two sisters means you have two female siblings. My sister’s car means the car belongs to one sister. My sisters’ house means the house belongs to two or more sisters.
This small apostrophe difference can change the meaning of an entire sentence. The guide below explains the rules, shows how to choose the correct form, and covers common mistakes in everyday English, academic writing, professional communication, and social media.
Quick Answer: Sisters or Sister’s?
The short rule
Sisters = more than one sister.
Sister’s = something belonging to one sister, or a contraction of sister is or sister has in informal writing.
Sisters’ = something belonging to two or more sisters.
| Form | Meaning | Example |
| sister | one female sibling | My sister lives nearby. |
| sisters | two or more female siblings | My sisters live nearby. |
| sister’s | belonging to one sister | My sister’s phone is ringing. |
| sisters’ | belonging to multiple sisters | My sisters’ phones are ringing. |
Memory tip: First decide how many sisters you mean. One sister → sister’s for possession. More than one → sisters’ for possession.
Oxford’s grammar guidance explains that regular plural nouns form possessives with an apostrophe after the plural s, while singular nouns normally take ’s.
What Does “Sister” Mean?
Definition of sister
A sister is a girl or woman who shares the same parents as another person. The word can also refer to a half-sister or, depending on context, a woman who has a close relationship with someone or belongs to the same group or organization. Cambridge and Oxford both recognize these broader uses.
Examples:
- My sister is a doctor.
- Sarah is my younger sister.
- She has one sister and two brothers.
- My best friend is like a sister to me.
The noun sister is singular when it refers to one person.
Why “sisters” is the plural
English usually forms the plural of a regular countable noun by adding -s. Therefore:
- one sister → two sisters
- one brother → two brothers
- one student → several students
- one teacher → several teachers
Cambridge gives examples such as Sophie and Emily are sisters and I’m one of three sisters.
The key point is that sisters does not contain an apostrophe when you simply mean more than one sister.
Examples in everyday English
- I have three sisters.
- My sisters are visiting this weekend.
- The two sisters started a business together.
- Her sisters live in different cities.
Key takeaway: Use sisters when the word is simply the plural noun and no possession is being expressed.
Sister’s vs. Sisters’: The Apostrophe Rule
The biggest source of confusion is the difference between sister’s and sisters’.
Sister’s means one sister owns or is connected to something
Use sister’s when one sister is the owner or when something is connected with one sister.
Examples:
- My sister’s car is new.
- I borrowed my sister’s jacket.
- My sister’s wedding is next month.
- That is my sister’s room.
- I attended my sister’s graduation.
In each sentence, there is one sister.
Compare:
My sister’s phone is broken.
The phone belongs to one sister.
Sisters’ means two or more sisters own or share something
Use sisters’ when two or more sisters possess or are associated with something.
Examples:
- My sisters’ cars are parked outside.
- The sisters’ bedroom is upstairs.
- We attended the sisters’ graduation ceremonies.
- The sisters’ business has grown quickly.
The apostrophe comes after the s because sisters is already plural.
My sisters’ house is beautiful.
This means the house belongs to, or is associated with, more than one sister.
A simple comparison
| Meaning | Correct form | Example |
| One sister | sister | My sister is here. |
| More than one sister | sisters | My sisters are here. |
| Belonging to one sister | sister’s | My sister’s bag is here. |
| Belonging to multiple sisters | sisters’ | My sisters’ bags are here. |
Oxford and Cambridge both describe this distinction as part of the standard possessive system: singular nouns generally take ’s, while regular plural nouns ending in s take an apostrophe after the s.
When to Use “Sisters”
Use “sisters” for a simple plural
If you are talking about two or more sisters without showing possession, write sisters.
Correct:
- They are sisters.
- I have two sisters.
- The sisters went shopping.
- Both sisters work as teachers.
- Her sisters live abroad.
Incorrect:
- I have two sister’s.
- They are sister’s.
- The sister’s went shopping.
The apostrophe is not used simply to make a noun plural.
A common misconception
Many learners see an apostrophe near the letter s and assume it indicates a plural. In standard English, that is not how ordinary plurals work.
Compare:
- cats = more than one cat
- cat’s = belonging to one cat
- cats’ = belonging to multiple cats
The same pattern applies to:
- sister → sisters → sister’s → sisters’
- teacher → teachers → teacher’s → teachers’
- student → students → student’s → students’
Key takeaway: Never add an apostrophe merely because a noun is plural.
When to Use “Sister’s”
Possession
The most common use of sister’s is to show that something belongs to one sister.
Examples:
- This is my sister’s laptop.
- I found my sister’s keys.
- My sister’s opinion matters to me.
- We went to my sister’s apartment.
Here, sister’s answers the question “Whose?”
Whose laptop? → My sister’s laptop.
Whose keys? → My sister’s keys.
“Sister’s” can also mean “sister is”
In informal English, ’s can be a contraction of is.
For example:
My sister’s coming home tonight.
This means:
My sister is coming home tonight.
Similarly:
My sister’s very busy.
means:
My sister is very busy.
“Sister’s” can also mean “sister has”
In some constructions, ’s can represent has.
For example:
My sister’s already left.
means:
My sister has already left.
Context tells you which meaning applies.
This is one reason sister’s can be confusing: it can indicate possession or function as a contraction. Oxford notes that possessive ’s and contracted forms of is or has have different grammatical functions.
When to Use “Sisters’”
Use it for plural possession
Use sisters’ when something belongs to or is associated with more than one sister.
Examples:
- The sisters’ parents live nearby.
- The sisters’ restaurant is popular.
- We visited the sisters’ childhood home.
- The two sisters’ opinions were very different.
Notice that the plural noun is already sisters, so the apostrophe is placed after the final s.
Compare singular and plural possession
Consider these two sentences:
My sister’s children are visiting.
This normally refers to the children of one sister.
My sisters’ children are visiting.
This normally refers to the children of two or more sisters.
That single apostrophe position changes the number of people connected to the noun.
Sisters, Sister’s, or Sisters’: A Decision Guide
Use this quick test whenever you are unsure.
Step 1: Are you talking about more than one sister?
Yes → Start with sisters.
Example:
My sisters live in Chicago.
No → Use sister.
Example:
My sister lives in Chicago.
Step 2: Does something belong to one sister?
Yes → Use sister’s.
My sister’s car is blue.
Step 3: Does something belong to several sisters?
Yes → Use sisters’.
My sisters’ cars are blue.
Step 4: Is “sister’s” actually short for “sister is” or “sister has”?
If the sentence makes sense after replacing ’s with is or has, it may be a contraction.
My sister’s tired.
→ My sister is tired.
My sister’s finished her homework.
→ My sister has finished her homework.
This four-step test prevents most errors.
Common Mistakes With Sisters and Sister’s
Mistake 1: Using an apostrophe to make “sisters” plural
Wrong:
I have two sister’s.
Correct:
I have two sisters.
Why? The sentence only needs the plural noun. There is no possession.
Mistake 2: Using “sister’s” when several sisters are involved
Wrong:
My sister’s are coming over.
Correct:
My sisters are coming over.
The verb are also provides a useful clue that the subject is plural.
Mistake 3: Using “sisters” for possession
Wrong:
My sisters car is outside.
Correct:
My sister’s car is outside.
The car belongs to one sister, so the possessive singular form is needed.
Mistake 4: Writing “sisters’s”
Wrong:
My sisters’s house
Correct:
My sisters’ house
Because sisters is already a regular plural ending in s, add only the apostrophe.
Mistake 5: Confusing “sister’s” with “sisters’”
Compare:
My sister’s children.
One sister’s children.
My sisters’ children.
Two or more sisters’ children.
The apostrophe position carries grammatical information.
How to Use These Forms in Professional and Academic Writing
Emails and workplace communication
The same rules apply in professional writing.
Correct:
I spoke with my sister yesterday.
Correct:
I need to attend my sister’s graduation.
Correct:
My sisters’ schedules are different.
There is no special business-writing rule that changes the apostrophe. What matters is grammatical number and possession.
Academic writing
Academic writing also follows the same distinction.
The study examined the experiences of three sisters.
No possession is expressed, so sisters is correct.
The researchers analyzed each sister’s response.
Each response belongs to one sister at a time, so sister’s is appropriate.
The sisters’ responses were compared.
The responses are associated with multiple sisters, so sisters’ is correct.
Social media and informal writing
Informal writing often uses shortened forms such as sis. Oxford lists sis as an informal abbreviation of sister.
Examples:
- Love you, sis!
- Happy birthday to my amazing sisters!
- My sister’s birthday is today.
The informal nature of sis does not change the basic possessive rules.
What About Sister-in-Law and Sisters-in-Law?
This is a related area where plural formation often causes mistakes.
The standard plural of sister-in-law is:
sisters-in-law
Not:
sister-in-laws
The reason is that the main noun is sister, so the plural marker attaches to sister.
Examples:
- I have two sisters-in-law.
- My sister-in-law lives nearby.
- My sisters-in-law are visiting.
Oxford specifically lists sisters-in-law as the plural form, while Cambridge explains that compounds such as brother-in-law form their plurals on the first noun.
For possession:
My sister-in-law’s car.
One sister-in-law owns the car.
My sisters-in-law’s cars.
Multiple sisters-in-law are associated with the cars.
The structure may look complicated, but the same number-and-possession logic still applies.
Related Words: Sister, Sibling, Sis, and Sisterhood
Sister vs. sibling
Sibling is a broader term. A sibling can be a brother or a sister. Cambridge defines sibling as a brother or sister.
Compare:
- I have three siblings. → Their genders are not specified.
- I have three sisters. → All three are female siblings.
Sister vs. sis
Sis is an informal shortened form of sister. It is common in casual speech, texts, and social media, but sister is the safer choice in formal writing.
Sisterhood
Sisterhood refers to the relationship or bond among sisters, and it can also describe solidarity among women.
This is different from sisters, which is simply the plural noun.
Expert Editing Tips for Choosing the Correct Form
A useful editing technique is to identify the grammatical job of the word before checking the apostrophe.
Ask:
- Am I naming one person? → sister
- Am I naming several people? → sisters
- Does something belong to one sister? → sister’s
- Does something belong to several sisters? → sisters’
- Could ’s mean “is” or “has”? → sister’s may be a contraction
Another useful test is the “whose?” test.
If the phrase answers whose?, you probably need a possessive:
Whose notebook? → My sister’s notebook.
Whose notebooks? → My sisters’ notebooks.
If you are simply counting people:
How many? → Three sisters.
This distinction is more reliable than trying to memorize isolated examples.
Mini Quiz: Can You Choose the Right Form?
Choose sister, sisters, sister’s, or sisters’.
- I have two ______.
- My ______ phone is ringing.
- My ______ are both doctors.
- The ______ house is on the corner. (one sister)
- The ______ house is on the corner. (several sisters)
- My ______ already finished the assignment. (has)
- Sarah and Emily are ______.
Answers
- sisters
- sister’s
- sisters
- sister’s
- sisters’
- sister’s
- sisters
The quiz highlights an important point: the same spelling, sister’s, can express possession or function as a contraction, depending on context.
Frequently Asked Questions
Is “sisters” grammatically correct?
Yes. Sisters is the standard plural of sister and means two or more sisters. For example, They are sisters is correct.
Is “sister’s” always possessive?
No. Sister’s can show possession, as in my sister’s car, but ’s can also be a contraction of is or has, as in my sister’s tired or my sister’s finished.
Is “sisters’” correct English?
Yes. Sisters’ is the plural possessive form. Use it when something belongs to or is associated with two or more sisters.
Should I write “my sisters” or “my sister’s”?
Use my sisters when referring to multiple sisters. Use my sister’s when referring to something belonging to one sister.
What is the plural of sister?
The plural is sisters. You do not need an apostrophe to make sister plural.
What is the possessive form of sisters?
The possessive form of the regular plural sisters is sisters’.
What is the possessive form of sister?
The singular possessive form is sister’s.
Is “sister’s” the same as “sisters”?
No. Sister’s can indicate possession or contraction, while sisters is simply the plural of sister. The apostrophe changes the grammatical function.
Which is correct: “my sisters’ names” or “my sister’s names”?
Both can be correct, but they mean different things. My sisters’ names means the names of multiple sisters. My sister’s names could mean the names associated with one sister, although the exact context would be needed to make that meaning clear.
Is “sister-in-laws” correct?
No, not in standard English. The usual plural is sisters-in-law.
Can “sisters” refer to people who are not biological sisters?
Yes. Sister can be used more broadly for close relationships, members of certain organizations or religious groups, and in other social contexts. Dictionaries record several such meanings.
Key Takeaways
- Sister = one female sibling.
- Sisters = two or more sisters.
- Sister’s = possession by one sister, or sometimes sister is/has.
- Sisters’ = possession by two or more sisters.
- Do not use an apostrophe to make sister plural.
- Use sisters-in-law, not sister-in-laws, for the standard plural.
- The easiest test is to ask “How many?” and “Whose?”
Editorial Note
The most common error with these forms is treating the apostrophe as a plural marker. In standard English, the apostrophe usually signals possession or contraction; it does not simply mean “more than one.” Checking the noun’s number first makes the correct form much easier to identify.
For formal writing, follow the standard grammatical distinction consistently. When a sentence feels ambiguous, rewrite it rather than relying on punctuation alone.
References
- Oxford Advanced Learner’s Dictionary: “sister”
- Oxford Learner’s Dictionaries: Possessive ’s and s’
- Cambridge Dictionary: “sister”
- Cambridge Dictionary: Possession and possessive ’s
- Cambridge Dictionary: Compound nouns and plurals
- Oxford Advanced Learner’s Dictionary: “sister-in-law”
Conclusion
Sisters, sister’s, and sisters’ are all correct forms, but they perform different grammatical jobs. Use sisters for more than one sister, sister’s for one sister’s possession or certain contractions, and sisters’ for possession involving multiple sisters.
The simplest rule to remember is: plural first, possessive second. Decide how many sisters you mean, then decide whether you need to show possession. Once you separate those two questions, the apostrophe becomes much easier to place correctly.
Actionable takeaway: Before writing sisters or sister’s, ask “How many?” Then ask “Whose?” That two-question check will solve most cases immediately.
David James is an English language enthusiast, writer, and author at StudyNixx, a website dedicated to helping readers understand confusing English words, spelling differences, and commonly mistaken word forms. He focuses on making English language learning simple, practical, and easy to understand.
David is also the author of two books on English language and word usage, where he explores common spelling mistakes, confusing words, and practical ways to improve written English. Through his writing and educational content, he helps students, writers, and everyday English learners choose the right words with confidence.
At StudyNixx, David covers common word comparisons such as summary vs. summery, shiny vs. shiney, spicy vs. spicey, and breached vs. breeched. His goal is to provide clear, useful, and reliable explanations that make English spelling and word usage easier for everyone.