What is a Temperature Converter?
A temperature converter changes values between Celsius (°C), Fahrenheit (°F), and Kelvin (K). Celsius and Fahrenheit are used for everyday weather, cooking, and body temperature, while Kelvin is the scientific standard used in physics and chemistry. Converting between them by hand is more involved than ordinary unit conversion, because temperature scales do not simply multiply into each other, so a reliable tool saves both time and errors.
Temperature conversion is a constant practical need. A weather forecast from the United States reports Fahrenheit while most of the world uses Celsius. A recipe gives an oven temperature in one scale or the other. Scientific reports use Kelvin. Understanding all three scales and moving between them correctly matters across travel, cooking, health, and study.
How to Use the Temperature Converter
Converting a temperature takes only a moment. Enter the value, choose the two scales, and read the result.
- Enter the temperature you want to convert in the “Temperature” field.
- Select the scale you currently have in the “From” dropdown.
- Select the scale you want in the “To” dropdown.
- Click “Convert” to see the result.
Conversion Formulas
These are the formulas behind the converter, which apply them automatically:
- Fahrenheit to Celsius: (°F – 32) × 5/9
- Celsius to Fahrenheit: (°C × 9/5) + 32
- Celsius to Kelvin: °C + 273.15
- Kelvin to Celsius: K – 273.15
- Fahrenheit to Kelvin and back are done by going through Celsius
The 273.15 offset in Kelvin conversions reflects the fact that absolute zero is 0 K, which equals -273.15°C.
Worked Conversion Examples
Here are three conversions worked out by hand using the formulas the converter applies automatically.
Celsius to Fahrenheit
A weather forecast says it will be 25°C and you want Fahrenheit. Multiply 25 by 9/5, which gives 45, then add 32 to get 77°F. A quick estimate is to double the Celsius value and add 30, which gives 80°F, close enough for planning.
Fahrenheit to Celsius
An oven setting reads 350°F and the recipe needs Celsius. Subtract 32 to get 318, then multiply by 5/9, which gives about 176.7°C. A common approximation is to subtract 30 and halve, giving 160, but the exact figure is more reliable for cooking.
Celsius to Kelvin
A chemistry experiment records 27°C. Add 273.15 to get 300.15 K. Because the Kelvin and Celsius degree sizes are identical, this conversion is a simple offset with no scaling.
Common Temperature References
These familiar reference points help you sanity-check any conversion:
- Water freezes: 0°C = 32°F = 273.15 K
- Room temperature: about 22°C = 72°F
- Body temperature: 37°C = 98.6°F
- Water boils: 100°C = 212°F = 373.15 K
- Absolute zero: -273.15°C = -459.67°F = 0 K
Understanding the Three Scales
Celsius
Celsius is the most widely used scale for everyday temperature. It is based on the freezing point of water at 0° and the boiling point at 100°, with one hundred equal degrees between them.
Fahrenheit
Fahrenheit is used mainly in the United States. It sets the freezing point of water at 32° and the boiling point at 212°, giving 180 equal degrees between them. Its finer granularity means whole-degree readings correspond to smaller temperature changes.
Kelvin
Kelvin is the scientific scale, starting at absolute zero, the coldest possible temperature where molecular motion nearly stops. There are no negative Kelvin temperatures, and the Kelvin degree is the same size as the Celsius degree.
When Are the Scales Equal?
A famous curiosity of temperature scales is that Celsius and Fahrenheit meet at -40 degrees. At exactly -40, the two scales read the same value: -40°C = -40°F. The converter demonstrates this correctly, and it is a great way to check that you understand the relationship between the scales.
Why Three Scales Exist
Each scale was created for a different purpose. Daniel Fahrenheit built his scale in the early 1700s, choosing the freezing point of a brine solution and the human body as reference points, which is why his scale uses such unusual-looking numbers. Anders Celsius later defined his scale around water, with 0° at freezing and 100° at boiling.
Lord Kelvin then added an absolute scale starting at the coldest physically possible temperature, which scientists need because many physical formulas require absolute temperature. The three coexist because each remains the most convenient for its own audience.
Mental Approximations
For quick estimates, doubling the Celsius value and adding 30 gives a rough Fahrenheit figure, accurate to within a few degrees for everyday ranges. To go the other way, subtract 30 and halve the Fahrenheit value. These shortcuts work well for weather and comfort checks, though they are not precise enough for science or cooking. Use the exact formulas in the converter whenever accuracy matters.
The shortcuts work because the exact conversion and the approximation diverge least in the comfortable 0–30°C range. The further you move toward extreme cold or heat, the larger the gap becomes, which is exactly when relying on the converter is safest.
Reading Temperatures in Different Contexts
- Weather: Celsius in most countries, Fahrenheit in the United States. A 20°C day and a 70°F day feel similar.
- Cooking: oven dials may use either scale depending on the country; check the unit before setting the temperature.
- Health: body temperature is normally around 37°C or 98.6°F, a useful reference for checking readings.
- Science: Kelvin is required in most physical formulas, so convert to it before doing calculations.
- Travel: knowing anchor points like 0°C freezing, 22°C comfortable, and 40°C hot makes forecasts in unfamiliar scales easier.
Why Use This Temperature Converter?
- All three scales in one tool
- Correct formulas applied automatically
- Instant results with no signup
- Free and unlimited use
- No data is ever uploaded
- Works on any device with a browser