If you're referring to Instagram engagement rate, it's usually measured as:
add the likes of all the last 10 photos/post
then, divide by 10.
Use that number and divide by total number of followers
= engagement rate
Now, be careful if you're looking at other accounts. Some play/buy fake likes. If an account has 10K followers and is getting 5K likes per photo, that is a Pinocchio account.
Great small/medium accounts (2k to 50k followers) get about 15%-20% engagement.
100k-1m accounts about 2%-7% engagement.
I've seen 10k follower accounts with 8k likes per photo. Talk about Kardashian body fake!