109°F to Celsius = 42.8°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

109 °F at a glance

Celsius: 42.78 °C
Exact fraction: 42 7/9 °C
Kelvin: 315.93 K
Rankine: 568.67 °R
Rounded: 43 °C
Quick estimate: 39.5 °C

How to convert 109 °F to Celsius

°C = (°F − 32) × 5/9
(109 − 32) × 5/9 = 77 × 5/9 = 385/9 = 42.78 °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. 77 is not a multiple of 9, so the exact answer is the repeating decimal 42 7/9 °C.

Estimate it in your head

Subtract 30 and halve: (109 − 30) ÷ 2 = 39.5 °C. That is 3.3 degrees low — the shortcut drifts at very hot and very cold temperatures, so use the exact formula there.

109 °F: extreme heat and hot water

Extreme heat. Air at 109 °F (42.78 °C) is dangerous even in dry climates; desert cities in the Southwest reach these readings on the hottest summer afternoons. Even at low humidity the heat index is high:

Relative humidity	Heat index	NWS category
10%	103 °F	Danger
25%	115 °F	Danger
40%	133 °F	Extreme danger

Too hot for a hot tub. 109 °F is above the 104 °F (40 °C) maximum the CPSC sets out for spa water, and well above any safe body temperature.
Food safety. 109 °F is still inside the 40–140 °F “danger zone” where bacteria grow fastest, so food kept warm at 109 °F is not being held safely.

Temperatures near 109 °F

Fahrenheit	Celsius	Kelvin
104 °F	40 °C	313.15 K
105 °F	40.56 °C	313.71 K
106 °F	41.11 °C	314.26 K
107 °F	41.67 °C	314.82 K
108 °F	42.22 °C	315.37 K
109 °F	42.78 °C	315.93 K
110 °F	43.33 °C	316.48 K
111 °F	43.89 °C	317.04 K
112 °F	44.44 °C	317.59 K
113 °F	45 °C	318.15 K
114 °F	45.56 °C	318.71 K

Going the other way: 43 °C in Fahrenheit is 109.4 °F.

Frequently asked questions

What is 109 °F in Celsius?

109 °F is 42.78 °C: subtract 32 (77) and multiply by 5/9.

Is 109 °F hot or cold?

109 °F is extremely hot — hotter than any healthy body temperature.

How do you convert 109 °F to Celsius in your head?

Subtract 30 and divide by 2: (109 − 30) ÷ 2 = 39.5 °C, compared with the exact 42.78 °C.

What is 109 °F in Kelvin?

109 °F is 315.93 K. Convert to Celsius (42.78 °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.

109 °F to °C

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