Below freezing, and just above it, everything goes on: a winter jacket or snowsuit over a warm sweater, lined trousers, wool socks, a warm hat, and mittens that turn fleece-lined below 1°C.
For a baby of 6–12 months on a still, dry day:
1°C (34°F): long-sleeve bodysuit, warm pants, warm socks, warm sweater, winter jacket, warm hat and mittens. Freezing — everything on, cover the hands. −15 – 0°C (5–32°F): long-sleeve bodysuit, warm pants, warm socks, warm sweater, winter jacket, warm hat and warm mittens. Freezing — everything on, cover the hands.
The NHS and the American Academy of Pediatrics both say one more layer than you would wear yourself. Thin layers under the jacket do more than one thick one, and they are easier to take off once you are inside.
In the car, the winter jacket comes off before the straps go on. Buckle the harness snug over thin layers and lay the jacket or a blanket over the top.
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 2°C, a winter jacket.
A warm hat outdoors below 15°C.
Mittens below 6°C, warm ones below 1°C.
0–3 months, −3°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, winter jacket, warm hat and warm mittens. 3–6 months, −3°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, winter jacket, warm hat and warm mittens. 6–12 months, −3°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, winter jacket, warm hat and warm mittens. 1–3 years, −3°C: long-sleeve bodysuit, warm pants, warm socks, warm sweater, winter jacket, warm hat and warm mittens.
Still and dry: Freezing — everything on, cover the hands. Windy (feels like −6°C (21°F)): No change Raining (feels like −4°C (25°F)): No change Sunny (feels like −1°C (30°F)): No change In a carrier (your warmth counts on the body): Winter jacket becomes blanket over the carrier In a car seat (no coat under the straps): Winter 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.