Translation guide
In Japanese, how you refer to your own grandpa versus someone else's, and how you address him directly, depends on formality, closeness, and family role. The most common and neutral term is おじいさん, but within the family, casual forms like おじいちゃん are typical.
You are talking to or about your own grandpa in a casual, family setting.
Affectionate, common term used by children and adults within the family. Can be used both to address him directly and to refer to him when talking to family members.
Grandpa, do you want to eat this?
More casual and slightly rough, often used by boys or in very informal family settings. Can sound affectionate or a bit blunt depending on tone.
Hey Grandpa, how are you?
Baby-talk or very affectionate term, often used by small children or when speaking to small children about their grandpa.
I love you, Grandpa!
You are talking about a friend's, colleague's, or stranger's grandfather.
You are talking about your own grandfather to someone outside the family, in a polite or formal setting.
Humble form used when speaking about your own grandfather to outsiders. Do not use to address him directly.
You are speaking to an old man you don't know, in a friendly or respectful way.
Grandpa is out for a walk right now.
Polite and standard way to refer to someone else's grandfather. Also used to address an elderly man you don't know well.
Mr. Tanaka's grandfather is very healthy, isn't he?
Very polite and respectful, often used in formal situations or when speaking to someone of higher status about their grandfather.
Please give my regards to your grandfather.
私の祖父は医者でした。
My grandfather was a doctor.
Common, friendly way to address an elderly man, similar to 'mister' or 'sir' but with a sense of his age. Can be used by anyone.
Are you okay, sir?
More affectionate, used by children or in a very warm, informal context. Can be condescending if used by adults to a stranger, so use with care.
Hey grandpa, you dropped this.
How old is your grandfather? (polite)
While おじいちゃん is affectionate for your own grandpa, using it for an unfamiliar elderly man can sound childish or overly familiar. Stick to おじいさん unless you know the person well.