−21°F to Celsius = −29.4°C

Fahrenheit to Celsius conversion table
°F	°C	Reference point
−40	−40	Both scales read the same
−20	−28.89
0	−17.78	Freezer setting
10	−12.22
20	−6.67
32	0	Water freezes
40	4.44	Refrigerator limit
50	10
60	15.56
65	18.33
68	20	Room temperature
70	21.11
72	22.22
75	23.89
80	26.67
85	29.44
90	32.22
95	35
97	36.11
98	36.67
98.6	37	Traditional normal body temp
99	37.22
100	37.78
100.4	38	Fever threshold
101	38.33
102	38.89
103	39.44
104	40	High fever
110	43.33
120	48.89
145	62.78	Whole cuts of beef, pork (USDA)
160	71.11	Ground meat (USDA)
165	73.89	Poultry (USDA)
212	100	Water boils at sea level
250	121.11
300	148.89
325	162.78
350	176.67	Moderate oven
375	190.56
400	204.44
425	218.33
450	232.22
500	260

−21 °F at a glance

Celsius: −29.44 °C
Exact fraction: −29 4/9 °C
Kelvin: 243.71 K
Rankine: 438.67 °R
Rounded: −29 °C
Quick estimate: −25.5 °C

How to convert −21 °F to Celsius

°C = (°F − 32) × 5/9
(−21 − 32) × 5/9 = −53 × 5/9 = −265/9 = −29.44 °C

Subtract 32 first because the two scales put zero in different places, then multiply by 5/9 because a Fahrenheit degree is only 5/9 the size of a Celsius degree. −53 is not a multiple of 9, so the exact answer is the repeating decimal −29 4/9 °C.

Estimate it in your head

Subtract 30 and halve: (−21 − 30) ÷ 2 = −25.5 °C. That is 3.9 degrees high — the shortcut drifts at very hot and very cold temperatures, so use the exact formula there.

What −21 °F feels like

Below zero Fahrenheit, wind matters more than the thermometer. The National Weather Service wind chill index estimates how cold −21 °F feels on exposed skin; once the wind chill reaches about −18 °F (−28 °C), frostbite can set in within 30 minutes.

Wind	Feels like	In °C	Note
10 mph	−42 °F	−41 °C	Frostbite possible in 30 min or less
20 mph	−50 °F	−45 °C	Frostbite possible in 30 min or less
30 mph	−54 °F	−48 °C	Frostbite possible in 30 min or less

At −29.44 °C even a home freezer (0 °F) would feel warm. Car batteries lose much of their cranking power, diesel fuel can gel without additives, and pipes in unheated spaces are at real risk.

Temperatures near −21 °F

Fahrenheit	Celsius	Kelvin
−26 °F	−32.22 °C	240.93 K
−25 °F	−31.67 °C	241.48 K
−24 °F	−31.11 °C	242.04 K
−23 °F	−30.56 °C	242.59 K
−22 °F	−30 °C	243.15 K
−21 °F	−29.44 °C	243.71 K
−20 °F	−28.89 °C	244.26 K
−19 °F	−28.33 °C	244.82 K
−18 °F	−27.78 °C	245.37 K
−17 °F	−27.22 °C	245.93 K
−16 °F	−26.67 °C	246.48 K

Going the other way: −29 °C in Fahrenheit is −20.2 °F.

Frequently asked questions

What is −21 °F in Celsius?

−21 °F is −29.44 °C: subtract 32 (−53) and multiply by 5/9.

Is −21 °F hot or cold?

−21 °F is severe cold, 21.0 degrees below zero Fahrenheit and well below freezing.

How do you convert −21 °F to Celsius in your head?

Subtract 30 and divide by 2: (−21 − 30) ÷ 2 = −25.5 °C, compared with the exact −29.44 °C.

What is −21 °F in Kelvin?

−21 °F is 243.71 K. Convert to Celsius (−29.44 °C) and add 273.15.

Need a different value? Use the Fahrenheit to Celsius converter, or browse the Fahrenheit to Celsius chart.

Sources: Wind chill and heat index use the US National Weather Service formulas. Health and food-safety thresholds are from the CDC, FDA, USDA, CPSC and US Department of Energy.

−21 °F to °C

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