My 3 month old is perfectly happy and healthy. She tracks the 9th percentile so is small but not concerning so (she was born on the 25th).
At night, she sleeps 11-12 hours bar 2 10 minute feeding wakes.
In the day however she is 100% NOT tired every hour and a half as the books say. She won't nap thar often: all thar happens is she is happily awake in the crib/sling/arms for another hour till she sleeps.
If I rock and put her down its always 3 times a day she has a good proper sleep.
It totals 13-14 hours - which many sources say is the lower end of ok.
She has no signs of over tiredness. GP, nurse and HV all state she is textbook healthy and we'll developed.
But some sources say 18 hours is ideal. They all say they can only go an hour and a half.
I feel so guilty and anxious: maybe she is 9% not 25% because she doesn't sleep enough. Maybe she will not develop properly. 
But when I look at HER it does seem she's sleeping enough for HER. And experienced mums nod and say "oh she's just a non napper ... does she sleep ok at night?" Which she does ... as if it's a harmless quirk. But am I neglecting her?
Sorry for the long rant. Anyone else feel this guilt or stress about the books (especially the sleep ones saying more is needed than the basic 14-16 hr most books say).