When shopping for a bathroom drain, there are a handful of things to consider. 

1. Check to make sure your bathroom faucet did NOT come with a bathroom drain. Usually, you'd like the two to match perfectly. Some manufacturers take the guess work out of it, and include the drain with the faucet. 
2. Does your sink have an overflow or is it a non-overflow? You NEED to know this to ensure you purchase the right drain.
3. While you're checking the overflow situation, get the drain hole size!
4. We recommend grid drains for those sinks that do NOT have an overflow. Why? Precaution to accidental flooding and the Sticky Bandits. #homealonereference