When trying to decide between two sizes, choose the larger size for a better fit.

SizeChestWaistHipsHeightWeight
3-9 Months17-1917-1917-1919 - 2613-19 lbs.
9-18 Months19-2119-2119-2127 - 3119-25 lbs.
18-24 Months21-2221-2221-2229 - 3322-30 lbs.