In the cold, the jacket comes on: below 10°C a baby lying still in a pram gets the outer layer a parent would wear, over a warm sweater. A hat is on throughout, and mittens join below 6°C.
For a baby of 6–12 months on a still, dry day:
6–9°C (43–48°F): long-sleeve bodysuit, warm pants, warm socks, warm sweater, jacket and warm hat. Cold — full outer layer and a hat. 2–5°C (36–41°F): long-sleeve bodysuit, warm pants, warm socks, warm sweater, jacket, warm hat and mittens. Cold — full outer layer and a hat.
"One layer more than you" is the rule the NHS and the AAP both give. A parent in this weather usually wears a coat over a jumper, so a baby who isn't moving wants the same three layers at least.
No coat or snowsuit under car seat straps. In the car seat the app puts a blanket over the buckled straps where the jacket would be.
Each piece comes on at its own temperature, a degree or two apart, so the outfit changes one piece at a time.
One light layer from 20°C, covered arms below.
Pants below 25°C (toddlers keep shorts to 21°C), lined ones below 13°C.
Socks below 24°C, warm ones below 12°C.
A sweater below 19°C, a warm one below 14°C.
Below 10°C: one layer more than you'd wear.
A warm hat outdoors below 15°C.
Mittens below 6°C, warm ones below 1°C.
0–3 months, 5°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, jacket, warm hat and mittens. 3–6 months, 5°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, jacket, warm hat and mittens. 6–12 months, 5°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, jacket, warm hat and mittens. 1–3 years, 5°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, jacket and warm hat.
Still and dry: Cold — full outer layer and a hat. Windy (feels like 2°C (36°F)): No change Raining (feels like 4°C (39°F)): No change Sunny (feels like 7°C (45°F)): Drops mittens In a carrier (your warmth counts on the body): Jacket becomes blanket over the carrier In a car seat (no coat under the straps): Jacket becomes blanket over the straps
Indoors, or in a warm car, bus or train, take the hat and outer layers off.
Check the neck — warm but not sweaty means just right.