Does a small baby mean less nappies?

My baby has just hit 4 weeks. She's gained her birth weight and is growing. While pregnant she was around the 9th percentile and currently she's around 2.4/2.5kg/5 lbs. Not preemie and she is healthy (thank god) but just naturally a small baby who grows slowly. I'm constantly worried that she's not hitting the 6-8 heavy wet and dirty nappy quota but I'm also wondering could this just be because she's smaller? She defintely has around 4-6 nappies but they're usually not heavy.