A temperature converter changes a reading between Celsius, Fahrenheit and Kelvin. You need it whenever a temperature is quoted in a scale you don't use day to day — following an American recipe in °F, reading a weather forecast abroad, setting an oven, or working with Kelvin in science. The three scales measure the same thing but start and step differently.
The formula. Conversions pass through Celsius as the base. From Celsius: °F = °C × 9/5 + 32 and K = °C + 273.15. Reversing them: °C = (°F − 32) × 5/9 and °C = K − 273.15. Here °C is degrees Celsius, °F is degrees Fahrenheit and K is kelvin. Celsius and Kelvin share the same degree size, while a Fahrenheit degree is smaller — 1 °C equals 1.8 °F.
Worked example. To convert a 180 °C oven to Fahrenheit, multiply by 9/5 and add 32: 180 × 1.8 + 32 = 356 °F. To express a comfortable 25 °C room in kelvin, add 273.15 to get 298.15 K. And a 98.6 °F reading is (98.6 − 32) × 5/9 = 37 °C.
Where it's used. Temperature conversion is part of daily life: ovens and air-conditioners are labelled in °C or °F depending on the country, weather apps toggle between the two, and fevers are read as 37 °C or 98.6 °F. Kelvin is standard in physics, chemistry and astronomy, and even describes the colour temperature of light bulbs (for example, 2700 K warm white).