When your baby is first born they will need from 10 to 12 diaper changes over a 24 hour period since they will be pooping and peeing more before they reach 1 year of age.
After 1 year of age your baby will pee less and poop less so will require fewer diaper changes per day.
For a newborn baby you should check there diaper at least every 30 to 40 minutes to see if it's wet or poop filled.
If it has poop it needs changed right away but if it's just a little wet then the diaper change can wait.
For an older baby over age 1 usually every 2 to 3 hours is good enough for changing diapers.
Some babies will let you know when they're wet or dirty and need changed and others won't care if they're wet or dirty so you really do need to check their diaper often.
A 2 year old or older child will usually only need 3 to 4 diaper changes per day but a younger baby might need around 5 to 7 diaper changes per day.