Temperature is the one common conversion you cannot do with a single multiplication, because the scales do not share a zero point. That is why the old trick of doubling Celsius and adding 30 works for a weather forecast but fails badly for an oven. This converter applies the exact formulas between Celsius, Fahrenheit, Kelvin and Rankine and shows the answer the moment you type.
It helps with oven dials, thermometers bought abroad, science homework, or simply knowing whether 30 degrees is hot. All four scales are listed together under the result, and everything runs locally on your device.
Four temperature scales and how they relate
Celsius places the freezing point of water at 0 °C and its boiling point at 100 °C at sea-level pressure. Fahrenheit, still standard in the United States, puts those same points at 32 °F and 212 °F, so 180 Fahrenheit degrees span what 100 Celsius degrees span. Each Celsius degree is therefore 1.8 Fahrenheit degrees, and the scales are offset by 32.
Kelvin is the SI scale used in science. It starts at absolute zero, the lowest possible temperature, and uses degrees the same size as Celsius, so 0 °C is 273.15 K and absolute zero is 0 K, or -273.15 °C. Rankine does the same for Fahrenheit: it starts at absolute zero with Fahrenheit-sized degrees, so absolute zero is 0 °R, or -459.67 °F. Rankine mostly appears in older American engineering and thermodynamics texts.
The formulas are °F = °C × 9/5 + 32 and °C = (°F - 32) × 5/9. Internally the tool converts every input to kelvin first and then out to the target scale, which keeps all four directions consistent.
When a temperature conversion helps
Oven and cooking temperatures
A European recipe that says 180 °C means 356 °F, which most American ovens would set as 350 °F. The reverse, 350 °F, is 176.666666667 °C, so 175 or 180 °C on a dial is the practical choice. Candy and frying thermometers are also often marked in only one scale.
Body temperature and fever
The traditional normal reading of 37 °C converts to exactly 98.6 °F. A reading of 100 °F is 37.7777777778 °C. Health guidance differs on where a fever begins, so use the converted number to follow the advice your doctor or local health service gives.
Weather and travel
A forecast of 25 °C is 77 °F, and 0 °F is a bitter -17.7777777778 °C. When you travel between countries that use different scales, a quick conversion makes forecasts and thermostat settings meaningful.
Science and engineering
Gas laws and radiation formulas require an absolute scale. Converting a lab reading of 20 °C to 293.15 K, or to 527.67 °R for imperial calculations, avoids the sign errors that come from using Celsius in a ratio.
What happens when you type a value
As you type in the Value field, the tool reads the number, converts it to kelvin using the formula for the unit chosen under From, then converts from kelvin to the unit under To. Floating-point noise is trimmed and up to 12 significant digits are shown, which is why fractions such as five ninths appear as 37.7777777778 rather than an endless string.
The swap button reverses the direction and puts the previous answer into the input, so you can check a conversion round trip. Below the main result, the All units table shows the same temperature in all four scales; clicking a scale name there sets it as the target. Negative numbers are accepted, so -40 works, and it is the one point where Celsius and Fahrenheit agree.
Cómo usar esta herramienta
- Type a temperature in the Value field, including a minus sign if it is below zero.
- Select the scale you are starting from in From, for example Celsius (°C).
- Select the scale you want in To, for example Fahrenheit (°F); the converted value appears at once.
- Check the All units table for Kelvin and Rankine too, and copy any value with its copy button.
Limitations
- Temperature differences are not the same as temperatures. A rise of 10 °C is a rise of 18 °F, but this tool converts readings, so entering 10 °C returns 50 °F. Multiply a difference by 1.8 instead.
- The tool does not stop you from typing a value below absolute zero, such as -300 °C. The result has no physical meaning.
- Historic scales such as Réaumur, Rømer and Delisle are not included.
- Values are rounded for display to 12 significant digits.