Feed on demand, make sure baby is having wet diapers, and the dr will do weight checks and if they are gaining they are getting enough.

There's no way to measure it. But if baby seems happy and content after feeds or falls asleep on the boob and is gaining weight, then baby is getting enough. Feeding on demand is the best way to ensure they're getting enough too instead of on a regulated schedule.

I always latched baby & let him unlatch himself when done. Don’t watch the clock. If baby wants more boob give baby boob.