Table 5.
The levels of physiological equivalent temperature (PET) and universal thermal climate index (UTCI)

Thermal perception	PET (°C)	UTCI (°C)	Grade of physiological stress
Very cold	⟨ 4	⟨ −40	Extreme cold stress
		−40 ∼ −27	Very strong cold stress
Cold	4 ∼ 8	−27 ∼ −13	Strong cold stress
Cool	8 ∼ 13	−13 ∼ 0	Moderate cold stress
Slightly cool	13 ∼ 18	0 ∼ 9	Slight cold stress
Neutral	18 ∼ 23	9 ∼ 26	No thermal stress
Slightly warm	23 ∼ 29		Slight heat stress
Warm	29 ∼ 35	26 ∼ 32	Moderate heat stress
Hot	35 ∼ 41	32 ∼ 38	Strong heat stress
Very hot	⟩ 41	38 ∼ 46	Very strong heat stress
		⟩ 46	Extreme heat stress