System design: Estimation | Users -> Daily active -> 10 times checking -> 250,000 per second

 Quite a bit. But I usually have the calculations handy. So like I’ll estimate users, then guess their number of API calls, then figure out the qps. Like Facebook news feed, 1 billion users, 250 million daily active, each checks their feed 10 times a day. There’s 2.5b calls, or 100m per hour, or 16m a minute, or 250,000 per second. Done.