我有一个哥哥。

Use this sentence exactly like you would in English. It follows a very logical flow. If you have two brothers, just swap 一个 for 两个 (liǎng gè). Remember to use 个 (gè) as the measure word. It is the most common 'counter' for people. It feels natural and effortless in almost any conversation.

Use it when you are meeting new friends or colleagues. It often comes up during 'small talk' about your background. You might say it while showing photos on your phone. It is also common in school settings or job interviews. Basically, any time your family tree is the topic, this is your go-to line.

Don't use 哥哥 if the brother is younger than you. For a younger brother, you must use 弟弟 (dìdi). Also, avoid using this if you are talking to your brother directly. You wouldn't say 'I have an older brother' to his face! That would be a bit awkward and confusing for everyone involved.

In Chinese culture, family titles are incredibly important. They show respect and define your place in the hierarchy. Even if you aren't related, you might call a close older male friend 哥哥. However, in this specific sentence structure, people will assume he is your biological sibling. It reflects a culture that deeply values kinship and clear social roles.

If you want to be more casual, you can drop the 一个 and just say 我有哥哥. If you have many, you could say 我有很多哥哥 (I have many older brothers). To ask someone else, just add 吗 (ma) at the end: 你有一个哥哥吗？ It is a very flexible pattern that grows with your vocabulary.