Early scan !! 4 weeks 4 days

Michelle • 33 year old from Australia , currently pregnant with baby #4 a boy..miss 7 mr 5 miss 1 and prince due 26/01/17
So my doctor ordered me to have a early scan due to bleeding and high hcg Levels , well I knew I would t see much just the sac , the tech said that's fine for this gestation , well it measured 5mm is that Normal range ? Anyone know ?