−21 °C at a glance
- Fahrenheit
- −5.8 °F
- Kelvin
- 252.15 K
- Rankine
- 453.87 °R
- Rounded
- −6 °F
- Quick estimate
- −12 °F
- As a change (Δ)
- Δ−21 °C = Δ−37.8 °F
How to convert −21 °C to Fahrenheit
−21 × 1.8 = −37.8
−37.8 + 32 = −5.8 °F
Multiply by 9/5 (1.8) because each Celsius degree spans 1.8 Fahrenheit degrees, then add 32 because water freezes at 32 °F rather than 0. The answer always has at most one decimal place, because multiplying a whole number by 1.8 can only leave tenths.
Estimate it in your head
Double it and add 30: −21 × 2 + 30 = −12 °F, which is 6.2 degrees low — good for weather, not for cooking or medicine.
Careful with temperature changes: a rise of 21 °C is a rise of 37.8 °F — multiply by 1.8 but do not add 32.
What −21 °C feels like
−21 °C is −5.8 °F. That is 3.0 degrees colder than a home freezer at −18 °C (0 °F). Environment Canada and the US National Weather Service both warn that frostbite can develop within 30 minutes once the wind chill reaches about −28 °C (−18 °F).
| Wind | Feels like | In °F | Note |
|---|---|---|---|
| 10 km/h | −28 °C | −19 °F | Frostbite possible in 30 min or less |
| 20 km/h | −32 °C | −25 °F | Frostbite possible in 30 min or less |
| 40 km/h | −35 °C | −32 °F | Frostbite possible in 30 min or less |
Temperatures near −21 °C
| Celsius | Fahrenheit | Kelvin |
|---|---|---|
| −26 °C | −14.8 °F | 247.15 K |
| −25 °C | −13 °F | 248.15 K |
| −24 °C | −11.2 °F | 249.15 K |
| −23 °C | −9.4 °F | 250.15 K |
| −22 °C | −7.6 °F | 251.15 K |
| −21 °C | −5.8 °F | 252.15 K |
| −20 °C | −4 °F | 253.15 K |
| −19 °C | −2.2 °F | 254.15 K |
| −18 °C | −0.4 °F | 255.15 K |
| −17 °C | 1.4 °F | 256.15 K |
| −16 °C | 3.2 °F | 257.15 K |
Going the other way: −6 °F in Celsius is −21.11 °C.
Frequently asked questions
What is −21 °C in Fahrenheit?
−21 °C is −5.8 °F: multiply by 1.8 (−37.8) and add 32.
Is −21 °C hot or cold?
−21 °C is severe cold — colder than a home freezer.
How do you convert −21 °C to Fahrenheit quickly?
Double it and add 30: −12 °F. The exact value is −5.8 °F.
What is −21 °C in Kelvin?
Add 273.15: −21 °C = 252.15 K.