Temperature converter
Convert between Celsius, Fahrenheit, and Kelvin.
Temperature Guide
Temperature Scales
The most common temperature scales are Celsius (°C), Fahrenheit (°F), and Kelvin (K). Celsius is used in most countries worldwide, including Poland and the European Union. Fahrenheit is used primarily in the United States, the Cayman Islands, the Bahamas, and Liberia. Kelvin is the absolute scale used in science and physics, where 0 K is absolute zero (-273.15°C).
History of the Fahrenheit Scale
Daniel Gabriel Fahrenheit created the temperature scale in 1724-1725. Originally 0°F was the coldest temperature he could achieve with a mixture of ice, salt, and water. Human body temperature is about 96°F in the original scale, today corrected to 98.6°F. Conversion: °F = (°C × 9/5) + 32.
Practical Applications
In cooking, Polish recipes use °C but American ones often use °F (350°F = 175°C, 375°F = 190°C, 400°F = 205°C). Baking requires precise temperature settings. Weather in Poland is given in °C, but vacations in the USA require knowing °F. Water boils at 100°C (212°F) at sea level, but only 69°C at the summit of Mount Everest.
−40 is the one temperature where Celsius and Fahrenheit agree
Converting temperature is unlike converting length or weight, because the two scales do not share a zero. Celsius puts zero at the freezing point of water, Fahrenheit puts it 32 degrees lower, and the degrees themselves are different sizes. That offset is why you cannot simply scale one into the other.
How it works
- Converts between Celsius, Fahrenheit and Kelvin, applying the offset as well as the ratio.
- Handles Kelvin correctly, which shares Celsius's degree size but starts at absolute zero.
- Makes the offset visible, which is what people get wrong when converting in their heads.
°F = °C × 9/5 + 32 °C = (°F − 32) × 5/9 K = °C + 273.15 the × 9/5 is the ratio of degree sizes the + 32 is the offset between the zeros — this is the part that is forgotten
Worked example
The reference points, and the single place the two scales meet.
- −40 °C = −40 °F
- 0 °C = 32 °F — water freezes
- 37 °C = 98.6 °F — body temperature
- 100 °C = 212 °F — water boils at sea level
−40 is the only temperature reading the same on both scales. Solving °C = °C × 9/5 + 32 gives exactly one answer, because two straight lines with different slopes cross exactly once.
Reading the result
- A degree Celsius is 1.8 times larger than a degree Fahrenheit, so a 5 °C rise is a 9 °F rise. For *differences* you use only the ratio and drop the offset entirely — adding 32 to a temperature change is a common and quietly wrong habit.
- Kelvin has no degree symbol and no negative values. It shares Celsius's step size, so a 1 K change and a 1 °C change are the same size; only the starting point differs.
- The quick mental version — double and add 30 — is close near room temperature and drifts badly at the extremes. At 20 °C it gives 70 against a true 68; at 100 °C it gives 230 against 212.
- Fahrenheit remains in everyday use in the United States and a handful of territories. Weather reports, oven settings and medical thermometers are the places the difference actually bites.
Common questions
- Why can't I just multiply to convert?
- Because the scales have different zero points. Multiplying alone works for units that share a zero, like metres and feet. Temperature needs the offset too, which is why 0 °C is 32 °F rather than 0 °F.
- Is there really only one temperature where they match?
- Yes, −40. The two conversions are straight lines with different slopes, and two such lines intersect at exactly one point. It is not a coincidence so much as a consequence.