−40°C to Fahrenheit = −40°F

Celsius to Fahrenheit conversion table
°C	°F	Reference point
−40	−40	Both scales read the same
−18	−0.4	Home freezer (about 0 °F)
−10	14
0	32	Water freezes
4	39.2	Refrigerator (40 °F or colder)
10	50
15	59
20	68	Comfortable room
22	71.6
25	77	Warm day
30	86	Hot day
35	95
37	98.6	Normal body temperature
38	100.4	Fever
40	104
50	122
60	140
74	165.2	Poultry cooked through (165 °F)
80	176
90	194
100	212	Water boils at sea level
120	248
140	284	Very low oven
150	302
160	320	Low oven
170	338
180	356	Moderate oven
190	374
200	392	Moderately hot oven
220	428	Hot oven
230	446
240	464	Very hot oven
250	482
260	500	Pizza / max home oven

−40 °C at a glance

Fahrenheit: −40 °F
Kelvin: 233.15 K
Rankine: 419.67 °R
Rounded: −40 °F
Quick estimate: −50 °F
As a change (Δ): Δ−40 °C = Δ−72 °F

How to convert −40 °C to Fahrenheit

°F = °C × 9/5 + 32
−40 × 1.8 = −72
−72 + 32 = −40 °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. Since −40 is a multiple of 5, the result is a whole number.

Estimate it in your head

Double it and add 30: −40 × 2 + 30 = −50 °F, which is 10 degrees low — good for weather, not for cooking or medicine.

−40 °C: where Celsius meets Fahrenheit

Plug −40 into the formula and the answer comes back unchanged: −40 × 1.8 + 32 = −72 + 32 = −40. Because Fahrenheit degrees are smaller, the Fahrenheit reading falls faster than the Celsius one as it gets colder, and the two lines on a graph cross at exactly −40.

At −40 °C, a standard 50/50 engine-coolant mix is at the edge of its protection (about −37 °C), exhaled breath freezes on scarves and eyelashes, and exposed skin can freeze in minutes in even a light wind:

Wind	Feels like	In °F	Note
10 km/h	−51 °C	−60 °F	Frostbite possible in 30 min or less
20 km/h	−56 °C	−68 °F	Frostbite possible in 30 min or less
40 km/h	−61 °C	−78 °F	Frostbite possible in 30 min or less

Temperatures near −40 °C

Celsius	Fahrenheit	Kelvin
−40 °C	−40 °F	233.15 K
−39 °C	−38.2 °F	234.15 K
−38 °C	−36.4 °F	235.15 K
−37 °C	−34.6 °F	236.15 K
−36 °C	−32.8 °F	237.15 K
−35 °C	−31 °F	238.15 K

Going the other way: −40 °F in Celsius is −40 °C.

Frequently asked questions

What is −40 °C in Fahrenheit?

−40 °C is −40 °F: multiply by 1.8 (−72) and add 32.

Is −40 °C hot or cold?

−40 °C is extreme cold, and the only temperature where a Celsius and a Fahrenheit thermometer show the same number.

How do you convert −40 °C to Fahrenheit quickly?

Double it and add 30: −50 °F. The exact value is −40 °F.

What is −40 °C in Kelvin?

Add 273.15: −40 °C = 233.15 K.

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

Sources: Wind chill and heat index use the US National Weather Service formulas; boiling points at altitude use the Antoine equation for water and the standard atmosphere. Health and food-safety thresholds are from the CDC, USDA, CPSC and US Department of Energy.

−40 °C to °F

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