21°F to Celsius = −6.1°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: −6.11 °C
Exact fraction: −6 1/9 °C
Kelvin: 267.04 K
Rankine: 480.67 °R
Rounded: −6 °C
Quick estimate: −4.5 °C

How to convert 21 °F to Celsius

°C = (°F − 32) × 5/9
(21 − 32) × 5/9 = −11 × 5/9 = −55/9 = −6.11 °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. −11 is not a multiple of 9, so the exact answer is the repeating decimal −6 1/9 °C.

Estimate it in your head

Subtract 30 and halve: (21 − 30) ÷ 2 = −4.5 °C. That is 1.6 degrees high, close enough to decide what to wear.

What 21 °F means in everyday life

Freezers. Home freezers should hold 0 °F (−17.8 °C), so 21 °F is 21 degrees warmer than a properly set freezer — still cold enough to keep ice solid.
Ice. At −6.11 °C, puddles, ponds and wet roads freeze. Rock salt melts ice well near 32 °F but works more and more slowly as pavement temperatures drop into the teens and below.
Wind chill. With wind, 21 °F feels much colder:

Wind	Feels like	In °C	Note
10 mph	10 °F	−12 °C	Dress in layers
20 mph	6 °F	−15 °C	Dress in layers
30 mph	3 °F	−16 °C	Dress in layers

Temperatures near 21 °F

Fahrenheit	Celsius	Kelvin
16 °F	−8.89 °C	264.26 K
17 °F	−8.33 °C	264.82 K
18 °F	−7.78 °C	265.37 K
19 °F	−7.22 °C	265.93 K
20 °F	−6.67 °C	266.48 K
21 °F	−6.11 °C	267.04 K
22 °F	−5.56 °C	267.59 K
23 °F	−5 °C	268.15 K
24 °F	−4.44 °C	268.71 K
25 °F	−3.89 °C	269.26 K
26 °F	−3.33 °C	269.82 K

Going the other way: −6 °C in Fahrenheit is 21.2 °F.

Frequently asked questions

What is 21 °F in Celsius?

21 °F is −6.11 °C: subtract 32 (−11) and multiply by 5/9.

Is 21 °F hot or cold?

21 °F is below freezing — water turns to ice and roads can be slick.

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

Subtract 30 and divide by 2: (21 − 30) ÷ 2 = −4.5 °C, compared with the exact −6.11 °C.

What is 21 °F in Kelvin?

21 °F is 267.04 K. Convert to Celsius (−6.11 °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

Show the work