Temperature converter
Convert temperatures between Celsius, Fahrenheit, and Kelvin instantly. Includes formulas and reference examples.
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Common temperature units
Celsius (°C)
Definition: Celsius (symbol: °C) is a temperature scale in which 0 °C is defined as the freezing point of water and 100 °C as its boiling point, both at standard atmospheric pressure (101.325 kPa). It is part of the International System of Units (SI).
History/origin: The scale was proposed by Swedish astronomer Anders Celsius in 1742. His original scale was inverted: 0 was boiling and 100 was freezing. It was later reversed by Carl Linnaeus and others to match today's convention. The unit was officially named "Celsius" in 1948.
Current use: Celsius is used in most countries of the world for everyday temperature measurement: weather forecasts, cooking, medicine, and science. It is the standard temperature unit in all countries except the United States, which primarily uses Fahrenheit.
Fahrenheit (°F)
Definition: Fahrenheit (symbol: °F) is a temperature scale where the freezing point of water is 32 °F and the boiling point is 212 °F at standard atmospheric pressure, a range of 180 degrees compared to 100 degrees in Celsius.
History/origin: Developed by German physicist Daniel Gabriel Fahrenheit in 1724. He based his scale on three reference points: the freezing point of a brine solution (0 °F), the freezing point of water (32 °F), and human body temperature (roughly 96 °F in his original scale).
Current use: Fahrenheit remains the official temperature scale in the United States for weather, cooking, and everyday use. It is also used in some Caribbean countries. Most other nations switched to Celsius during metrication in the 20th century.
Kelvin (K)
Definition: Kelvin (symbol: K) is the SI base unit of thermodynamic temperature. It uses the same degree size as Celsius but starts at absolute zero, the theoretical lowest possible temperature, which is 0 K (equivalent to -273.15 °C).
History/origin: Named after the British physicist William Thomson, 1st Baron Kelvin, who first proposed the absolute temperature scale in 1848. Unlike Celsius and Fahrenheit, Kelvin has no negative values, making it the natural scale for thermodynamic calculations.
Current use: Kelvin is used primarily in science and engineering, particularly in physics, chemistry, astrophysics, and cryogenics. It is the standard for expressing temperatures in scientific literature. Room temperature is approximately 293-295 K.
Common temperature reference points
| Reference point | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) |
|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 |
| Water freezing point | 0 | 32 | 273.15 |
| Room temperature | 20-22 | 68-71.6 | 293-295 |
| Human body temperature | 37 | 98.6 | 310.15 |
| Water boiling point | 100 | 212 | 373.15 |
| Oven (moderate) | 180 | 356 | 453.15 |
How to convert temperature units
Unlike most unit conversions, temperature scales are not related by simple multiplication because they each have a different zero point. The formulas below account for both the scale difference and the offset.
Celsius to Fahrenheit
°F = (°C × 9/5) + 32
Example: 25 °C = (25 × 9/5) + 32 = 77 °F
Fahrenheit to Celsius
°C = (°F - 32) × 5/9
Example: 98.6 °F = (98.6 - 32) × 5/9 = 37 °C
Celsius to Kelvin
K = °C + 273.15
Example: 100 °C = 100 + 273.15 = 373.15 K
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5 (or 1.8) then add 32. For example, 20°C = (20 × 1.8) + 32 = 68°F. A quick mental shortcut: double the Celsius temperature and add 30 for a rough Fahrenheit estimate (20°C → 40 + 30 = 70°F, close to the exact 68°F).
How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, 98.6°F = (98.6 − 32) × 5/9 = 66.6 × 0.5556 = 37°C. Key reference points: 32°F = 0°C (freezing), 72°F ≈ 22°C (room temperature), 98.6°F = 37°C (body temperature), 212°F = 100°C (boiling).
What temperature is the same in Celsius and Fahrenheit?
The two scales meet at exactly −40°. That is, −40°C = −40°F. This is a useful sanity check when converting very cold temperatures: if your result near −40 doesn't match between the two scales, the conversion is wrong.
How do I convert Celsius to Kelvin?
Add 273.15 to the Celsius value. For example, 100°C = 373.15 K, and 0°C = 273.15 K. Absolute zero (0 K) equals −273.15°C — the theoretical lowest possible temperature. Kelvin uses the same degree size as Celsius but starts at absolute zero, so there are no negative Kelvin values.
What is a normal body temperature in Celsius and Fahrenheit?
Normal human body temperature is 37°C (98.6°F). A fever is generally defined as above 38°C (100.4°F). These values are oral temperature readings; rectal and ear temperatures run slightly higher, and armpit temperatures slightly lower.
What are common oven temperatures in Celsius and Fahrenheit?
Common oven temperature conversions: 150°C = 300°F (low/slow), 180°C = 356°F (moderate, most baking), 200°C = 392°F (moderately hot), 220°C = 428°F (hot), 250°C = 482°F (very hot). Most baking recipes that originate in the US use Fahrenheit; European and UK recipes use Celsius.
Related articles
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Celsius to Fahrenheit Oven Conversion: How to Convert Cooking Temperatures CorrectlyNeed to convert Celsius to Fahrenheit for baking or roasting? This practical oven temperature guide explains the formulas, the most common conversions, and how to avoid ruined recipes.