| Zone | SSI value (˚F) | Perceived Thermal Sensation | Symbol |
| 1 | 70 ≤ SSI < 77 | Most people are comfortable, but slightly cool | A |
| 2 | 77 ≤ SSI < 83 | Nearly everyone feels quite comfortable | B |
| 3 | 83 ≤ SSI < 91 | Most people are comfortable, but slightly warm | C |
| 4 | 91 ≤ SSI < 100 | Increasing discomfort(warm) | D |
| 5 | 100 ≤ SSI < 112 | A caution of sunstroke and heat exhaustion exists for prolonged exposure and activity, along with significant discomfort (extremely warm) | E |
| 6 | 112 ≤ SSI < 125 | Virtually everyone is uncomfortable, a danger of heatstroke and great discomfort exists (hot) |
F |
| 7 | 125 ≤ SSI < 150 | There is an extreme danger of heatstroke, especially for the weakened or elderly, and even young children. Maximum discomfort exists at these conditions (extremely hot) | G |
| 8 | 150 < SSI | Circulatory collapse is imminent for prolonged exposure |
H |