40 degrees Celsius = 104.00°F (313.15 K). Use the copy buttons below for any format, or enter a custom value in the converter.
The Celsius scale sets 0°C at the freezing point of water and 100°C at its boiling point. The Fahrenheit scale, used primarily in the United States, sets those same points at 32°F and 212°F. To convert Celsius to Fahrenheit, multiply by 9/5 and add 32: °F = (°C × 9/5) + 32. For 40°C: (40 × 1.8) + 32 = 104.00°F.
40°C
104.00°F
313.15 K
Fahrenheit
104.00°F
Kelvin
313.15 K
Full (°C to °F)
40°C = 104.00°F
Full (°C to K)
40°C = 313.15 K
High fever / dangerous heat
40°C (104°F) represents both a high fever requiring medical attention and an extreme heat wave. Heat stroke risk rises sharply for outdoor workers and the elderly at this air temperature.
Enter any Celsius value to convert it live to Fahrenheit and Kelvin.
Here are three everyday situations where knowing that 40°C = 104.00°F makes a practical difference.
If a recipe involves simmering, fermenting, or proofing at 40°C, that's 104.00°F. For example, bread dough proofing at 25–30°C, chocolate tempering at 31–32°C, and sous-vide cooking at 55–65°C all require precise Celsius-to-Fahrenheit conversions when using US kitchen tools.
You're checking the weather for a trip abroad and the forecast shows 40°C. That's 104.00°F. Light, breathable clothing and sun protection are a must. Most weather apps let you switch between °C and °F, but knowing the conversion helps when reading local signage or talking to locals.
In a chemistry or physics class, temperatures are often given in Celsius and need to be converted for US-format worksheets, or converted to Kelvin for thermodynamics problems. 40°C = 104.00°F = 313.15 K. The Kelvin scale is used in the ideal gas law (PV = nRT) and other thermodynamic equations where absolute zero (0 K = −273.15°C) is the reference point.
See how 40°C compares to nearby temperatures in both Celsius and Fahrenheit.
Common questions about 40°C and its Fahrenheit equivalent, answered.