Mine was measured as 3 on one side and 3.5 on the other, but she is wearing size 4F, soft-soled shoes on the advice of the fitter, and she's doing great with them. It's definitely best to get them professionally measured as for kids (at least in the UK) they measure width as well as length - the 'F' part is the width of her foot. They can also check that your babies' feet are comfortable in their shoes and have room to grow.