"May I have" is very polite. "Can I get" is casual. May I have another piece of cake? Can I get two tickets to the concert?

In British English - 'May I have' is correct. (obviously followed by a 'Please') May I have a glass of water please? 'Can I get' is more an informal American term, and can come across in the UK as rather impolite, depending on it's usage.

In natural conversations there isn't much of a difference! "May I have..." is more polite, however most people will just say "Can I get..." Both mean asking for something, and have the same meaning :) "Can I get..." is more natural in almost any case. But if you're in a more formal setting, use "May I get..." Some examples: 1. Can I get a glass of water? 2. May I have a glass of water?

"May I have..." is considered to be really polite. If you are talking to a stranger and want to be polite then you can say this. "Can I get..." is just the normal way of saying you want something. e.g. The difference between "Can I get a glass of water?" and "May I have a glass of water?" is just politeness