I'm a paediatrician. No parent has ever asked me for their baby's weight in kg - they are all pounds and ounces. So much so that I can do this niche conversion almost in my head, at least at the start of the day, as we weigh them in kg.

What's weird is my pediatrician here in Seattle uses kg for my ~10 year old kids' weights but inches for their heights. Why the kg? They always translate to pounds for discussion, but the record is in kg.

It was always pounds and ounces when they were babies though. Not sure when it switched to kg; probably when we switched from "baby specialist" to "standard pediatrician" so around toddler age.

Yes, I've never heard a baby weight given in Kg.

But it seems to change when people are old enough to be talking about their own weight.

SI has been the standard for decades in Australia, but people almost always ask for baby weights in pounds and ounces.

Adult heights are the other exception, those are often in feet and inches. My 14 year old knows she's 5'2" but her knowledge of imperial measurements doesn't go much further than that.