What is the formula to convert C to F?
°F = (°C × 9/5) + 32, or equivalently °F = (°C × 1.8) + 32.
Temperature calculator
Temperature converter
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Temperature measures the average kinetic energy of particles in matter. Three scales are in common use: Celsius (°C), the international standard; Fahrenheit (°F), used in the US; and Kelvin (K), the SI base unit for science. Water freezes at 0°C = 32°F = 273.15 K and boils at 100°C = 212°F = 373.15 K at sea-level pressure.
Example temperature conversions
-40°C-40°F (scales cross)
0°C32°F, 273.15 K (water freezes)
10°C50°F
20°C68°F (room temperature)
Open the live temperature converter for any input value.
The three temperature scales
The Celsius scale puts the freezing point of water at 0° and the boiling point at 100°. It was originally proposed by Anders Celsius in 1742 with the scale inverted, but Linnaeus and others flipped it to its modern form. The Fahrenheit scale, proposed by Daniel Gabriel Fahrenheit in 1724, places water's freezing point at 32°F and boiling at 212°F. The 180-degree gap between freezing and boiling makes Fahrenheit feel finer-grained in everyday use, which is one of the arguments US holdouts make for keeping it.
The Kelvin scale is Celsius shifted to absolute zero: 0 K = -273.15°C, the temperature at which classical particle motion stops. Kelvin uses the same degree size as Celsius, so a 10 K temperature change equals a 10°C change. Scientific publications, especially in physics and chemistry, almost always use Kelvin.
Conversion formulas
Celsius to Fahrenheit: °F = (°C × 9/5) + 32. Fahrenheit to Celsius: °C = (°F − 32) × 5/9. Celsius to Kelvin: K = °C + 273.15. Kelvin to Celsius: °C = K − 273.15. Fahrenheit to Kelvin: K = (°F − 32) × 5/9 + 273.15.
There's one elegant coincidence in the C-F conversion: -40°C equals -40°F exactly. It's the single temperature where the two scales cross, useful for sanity-checking conversion code.
Practical reference points
For weather and everyday comfort: 0°C / 32°F is freezing; 20°C / 68°F is a comfortable indoor temperature; 30°C / 86°F is a warm day; 40°C / 104°F is a heatwave. For cooking and HVAC: 180°C / 356°F is a moderate oven; 200°C / 392°F is a hot oven; 100°C / 212°F is water's boiling point at sea level (lower at altitude, since lower pressure reduces the boiling point).
For health and biology: normal human body temperature is 37°C / 98.6°F, with healthy daily variation between about 36.1°C (97°F) and 37.2°C (99°F). Hyperthermia begins around 38°C (100.4°F); hypothermia begins around 35°C (95°F).
Common temperature conversions
| From | Equivalent |
|---|---|
| -40°C | -40°F (scales cross) |
| 0°C | 32°F, 273.15 K (water freezes) |
| 10°C | 50°F |
| 20°C | 68°F (room temperature) |
| 25°C | 77°F |
| 37°C | 98.6°F (body) |
| 100°C | 212°F, 373.15 K (water boils) |
| 180°C | 356°F (oven) |
| 0 K | -273.15°C, -459.67°F (absolute zero) |
Frequently asked questions
What is normal human body temperature?
37°C or 98.6°F. Healthy individuals range from about 36.1°C (97°F) to 37.2°C (99°F) depending on time of day, age, activity, and the measurement site.
Why does Kelvin not use the degree symbol?
By SI convention, kelvin is a base unit name and is written without 'degrees' or the ° symbol: '300 K', not '300°K'.
What is absolute zero?
0 K, equivalent to -273.15°C or -459.67°F. It's the theoretical temperature at which all classical thermal motion stops. The third law of thermodynamics says you can approach it but never quite reach it.
Why does water boil at a lower temperature at altitude?
Boiling occurs when a liquid's vapor pressure equals the surrounding atmospheric pressure. At higher altitude, atmospheric pressure is lower, so water boils at a lower temperature. At 2,400 m (8,000 ft) elevation, water boils around 91°C / 196°F instead of 100°C / 212°F.
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