The sizing on commercial baby clothing is unreliable, and handmade baby knitwear is worse. A "3-6 months" label from a Dutch pattern and a "3-6 months" label from a British pattern can produce pieces that differ by several centimetres in every direction. We've seen this enough times that we now ignore age labels almost entirely when taking a new order.
What we work with instead are measurements. This note explains which ones matter, how to take them, and the situations where no measurement will save you — which is mostly gift orders for unborn babies.
For hats: head circumference is the only number that matters
Take a soft tape measure around the widest part of the head, roughly 2 centimetres above the ears. That number, in centimetres, is what we work from. We don't need the age. We don't need the weight or height. Head circumference is the one measurement that translates directly into a hat that fits.
Common ranges, for reference: newborns run 32-36cm, 3-6 months is roughly 40-44cm, 12 months around 46-48cm. But these overlap significantly because babies are not standard. A three-month-old with a 44cm head needs a different hat than a three-month-old with a 40cm head.
We knit with 2-3cm of ease built in — enough that the hat sits comfortably without squeezing, not so much that it falls over their eyes.
For rompers and overalls: three measurements
Body length (nape of neck to crotch), chest circumference (around the widest point), and inseam length (crotch to ankle) if it's a full-length overall rather than a shorties. Weight is helpful as a cross-reference but it's the measurements we knit to.
We ask for these and then apply ease based on the silhouette. Structured overalls get less ease than relaxed ones. Pieces intended to fit over a nappy get more ease in the body. We'll discuss this during the order conversation — it's not something you need to calculate in advance.
When measurement doesn't help: gifts for unborn babies
If someone is ordering a gift and the baby hasn't arrived yet, there's nothing to measure. This comes up regularly. Our default is to knit larger than a standard "newborn" size — usually a 3-month size — because it's easier to roll up a sleeve than to explain why a hat lasted three weeks.
For gift pieces specifically, we almost always recommend a hat rather than a romper. Hats are more forgiving of size variation and last longer in terms of fit. A well-made merino hat can be worn from one month to six months with the same head, just differently positioned on the head as the child grows.
A word about patterns that specify size by months
When someone comes to us with a pattern they want knitted, the age ranges on those patterns are often based on the designer's own children, or a sample set of two or three. They're starting points. If the measurements given in the pattern (most patterns do include them in a table) don't match the baby in front of you, the measurements win. Adjust the pattern to match the measurements, not the other way around. This is one of the things we go through in the workshops — it's not complicated but it requires ignoring what the pattern says it's for.