How long should a 20 week old sleep during the day approx?

[milkyman]

My 20 week old boy's sleep was really bad this week (it's never been great but this week was worse). He was waking up at 1, 3, 5 etc... Last night he woke up at 4:20am only (hurrah!). He didn't have many naps in the day preceding this as we were out and about. Would this be the reason or is it a coincidence? He slept for about 2.5 hrs when he usually naps for approx. 4 hrs.

Maybe he's ready to wean? I know guidelines say 6 months, but some babies are ready earlier than others. It may be he's waking due to being hungry?
Otherwise, babies do change sleeping patterns but all the books say that a 20 week old should be sleeping for about 14hours total per day. I've copied and pasted the below chart for you from the baby centre website. Hope it helps.
How much sleep does your baby need?

Age Daytime sleep Night-time sleep Total sleep
Newborn 7hrs 30mins (3 naps) 8hrs 30mins 16 hrs
One month 6hrs 45mins (3 naps) 8hrs 30mins 15hrs 15mins
Two months 5hrs 30mins (3 naps) 10hrs 15hrs 30mins
Three months 5hrs (3 naps) 10hrs 15hrs
Six months 3 hrs (2 naps). 11hrs 14hrs
Nine months 2hrs 45mins (2 naps) 11hrs 15mins 14hrs
12 months 2hrs 15mins (2 naps) 11hrs 30mins 13hrs 45mins

My DD is about 23 weeks and for the last couple of months she only has about 40mins to an hour during the day, spread over two naps.
She sleeps better at night with less sleep during the day.
Was the total opposite for DS. If he had long naps he slept better at night.

They won't make anything easy!