Wind chill. The feels-like figure uses the JAG/TI wind-chill formula, which estimates how cold exposed skin feels in moving air. It is defined for temperatures at or below 10 °C and winds above 4.8 km/h; above that the page just shows the air temperature rather than inventing a number. Wind chill does not make a costume colder — it strips heat from the skin that is exposed, which is why a mask and gloves matter out of proportion to their thickness.

Insulation. Clothing insulation is measured in clo; 1 clo is roughly a business suit, 0.5 clo a light shirt. A thin costume is about 0.35 clo, a covered one about 0.65, and a padded suit about 0.95. Each layer underneath adds 0.15. Wet fabric loses roughly 30% of its insulation, so rain is applied as a multiplier rather than added as a separate number.

Heat balance. The page estimates dry heat loss from the skin to the air — temperature difference divided by the insulation of the clothing plus the still-air layer around it — and subtracts that from the heat a body makes: about 60 W/m² standing, 100 walking, 140 at a party. A positive balance means the body is making more heat than it loses (comfortable or warm); a negative one means it is losing heat and will cool down. The comfortable band is deliberately wide because children run hot when excited and cold when tired.

What it cannot tell you. It does not model rain soaking through in real time, wind gusts, individual circulation, or the effect of a costume that traps heat while standing and vents while running. It is a dressing guide, not a safety limit: if a child is shivering, unusually quiet or has cold, pale hands, the evening is over regardless of what the numbers say.

Last reviewed: 2026-10-20. General comfort guidance for healthy people; seek medical advice for hypothermia symptoms and take extra care with babies and older adults.