Work out clothing layers for temperature instantly with clear inputs, formula shown and shareable results.
Wind chill is computed with the standard formula, insulation need is roughly one clo per ten degrees below 33 C skin temperature, and activity heat is subtracted before dividing by about 0.8 clo per layer. Activity is the biggest variable: running generates enough heat to replace nearly two layers, which is why dressing for the start of a run leaves you overheating.
Wind chill
chill = 13.12 + 0.6215T - 11.37 v^0.16 + 0.3965 T v^0.16, for T <= 10 C and v >= 4.8 km/h
Layers
layers = ceiling(((33 - chill) / 10 - activity clo) / 0.8)
chill = 13.12 + 0.6215T - 11.37 v^0.16 + 0.3965 T v^0.16, for T <= 10 C and v >= 4.8 km/h. Wind chill is computed with the standard formula, insulation need is roughly one clo per ten degrees below 33 C skin temperature, and activity heat is subtracted before dividing by about 0.8 clo per layer.
Activity is the biggest variable: running generates enough heat to replace nearly two layers, which is why dressing for the start of a run leaves you overheating.
Enter air temperature, wind speed, activity level. The defaults shown are a realistic worked example — swap in your own figures to get a result you can use.