Three scales, one number, no mental arithmetic
Convert °C to °F, °F to °C or either to Kelvin. Built for ovens, weather forecasts and lab work where the difference actually matters.
Temperature trips people up because it is the one conversion that is not a simple multiplication. Celsius and Fahrenheit start counting from different places, so you have to shift before you scale.
The formula is °F = °C × 9/5 + 32. That +32 is why the popular 'double it and add 30' shortcut drifts badly at oven temperatures — at 200 °C it is off by 38 degrees.
The converted temperature across Celsius, Fahrenheit and Kelvin Instant results for oven settings, forecasts and scientific readings Correct handling of negatives, where the shortcut methods fall apart Kelvin shares Celsius's step size but starts at absolute zero: 0 K = −273.15 °C. This converts temperature readings, not temperature differences — a rise of 10 °C is a rise of 18 °F, not 50 °F. What is 180 °C in Fahrenheit? 356 °F. Recipes almost always round it to 350 °F, which is the standard American moderate-oven setting.
At what temperature do Celsius and Fahrenheit read the same? −40. It is the one point where the two scales cross, so −40 °C and −40 °F are the same cold.
Why doesn't 'double it and add 30' work for cooking? It approximates ×1.8 with ×2, so the error grows with the number. At 20 °C it is 2 degrees out; at 200 °C it is 38 degrees out, which is the difference between roasting and burning.
Should I write K or °K? K on its own. Kelvin is an absolute scale, so it does not take the degree symbol — 300 K, never 300 °K.
Worked example An American recipe in a European oven
Input: 425 °F → Celsius
Output: 218.3 °C
Note: Most European ovens step in 10s, so you would set 220 °C. The 1.7-degree difference is far smaller than the swing of a domestic oven thermostat.
