Because baby sizes aren’t standardized, a couple of measurements will almost always tell you more than the age printed on a tag. The good news is you only really need two, and neither calls for precision.
Weight is the most useful single number. Most size charts are built around it, and it’s usually the closest guide to whether a piece will fit now. Height, or length, is the helpful second — it’s what tends to decide whether sleeves and legs land right, especially on rompers and sleepers, where length runs out before width does.
At home, a soft tape measure along the length while baby is lying calm, and a recent weight — from a check-up, or by stepping on a scale holding baby and subtracting your own — is plenty. There’s no need to fuss over a centimetre.
With those two numbers, a brand’s size chart becomes far more reliable than guessing by month. And when a measurement sits between two sizes, sizing up is the usual instinct — a little room is easy to grow into, and gentler than a piece outgrown in a fortnight.
Measure once, note it somewhere, and shopping gets quietly easier — you’re buying for the baby in front of you, not the number on the calendar.
