My 12 months 2 weeks old has head size 30%, is that normal?

My 12 months old has weight 50%, length 80% and head size 30%, is that OK?? I worried about his head size, is that too small? he is doing all normal activites, response normal. He shows his tummy when I ask it for, do clapping when I ask it for. But worried, because his head size is smaaler then 50%. Any advice on can it effect my baby anyway??