If I eventually give in to peer pressure and drink, how do I know when to stop?

I’m 16 and I’ve been going to parties where there’s alcohol. I don’t currently drink, and I’ve been refusing whenever people try to get me to.

The problem is that the peer pressure is pretty persistent, and realistically I don’t know if I’ll keep saying no forever. I don’t want my only plan to be “I won’t drink,” because if I eventually give in, I’ll have basically zero experience and zero idea where my limit is.

So I’m asking from a harm-reduction perspective: if I do end up drinking at a party, how can I recognize that I’ve had enough before I’m seriously drunk or sick?

What early warning signs should I pay attention to? How do you avoid accidentally drinking too quickly before the alcohol fully hits you? And if you realize you’ve already had too much, what should you do?

I’d rather know this beforehand than make decisions with no information while I’m already at a party.