Temperature Converter for Celsius, Fahrenheit and Kelvin Online
Convert Celsius, Fahrenheit, and Kelvin instantly with live results, quick unit swaps, and common reference temperatures.
Convert Temperature
Enter a temperature, choose the starting scale, and select the scale you want.
How to Use the Temperature Converter
The temperature converter changes a value between Celsius, Fahrenheit, and Kelvin. Enter the temperature, choose the starting scale, then select the scale you want. The result updates instantly.
- Enter a temperature. Negative values are allowed where physically valid.
- Select the starting scale. Choose Celsius, Fahrenheit, or Kelvin.
- Select the target scale. The converted result appears immediately.
- Use Swap Units. Reverse the two selected scales without retyping the value.
- Check all scales. The result panel also shows the same temperature in all three systems.
Shortcut buttons make common conversions such as Celsius to Fahrenheit and Fahrenheit to Celsius faster to select.
How Temperature Conversion Works
Temperature conversion is different from many unit conversions because the scales do not all begin at the same zero point. Celsius and Fahrenheit require both multiplication and an offset. Kelvin uses the same interval size as Celsius but starts at absolute zero.
The calculator converts the entered value through Celsius internally, then converts that value to the requested scale.
Temperature Conversion Formulas
°F = (°C × 9 ÷ 5) + 32
°C = (°F - 32) × 5 ÷ 9
K = °C + 273.15
°C = K - 273.15
How to Convert Celsius to Fahrenheit
Multiply the Celsius value by 9/5, then add 32.
25 °C to Fahrenheit
(25 × 9 ÷ 5) + 32 = 77 °F
Water freezes at 0 °C, which equals 32 °F. Water boils at 100 °C, which equals 212 °F at standard atmospheric pressure.
How to Convert Fahrenheit to Celsius
Subtract 32 from the Fahrenheit value, then multiply by 5/9.
68 °F to Celsius
(68 – 32) × 5 ÷ 9 = 20 °C
This formula is useful for weather, room temperature, cooking references, and international temperature comparisons.
How to Convert Celsius to Kelvin
Celsius and Kelvin have the same size interval. The difference is their zero point. Add 273.15 to a Celsius value to convert it to Kelvin.
K = °C + 273.15
20 °C to Kelvin
20 + 273.15 = 293.15 K
How to Convert Kelvin to Celsius
Subtract 273.15 from Kelvin to get Celsius.
°C = K - 273.15
300 K to Celsius
300 – 273.15 = 26.85 °C
How to Convert Fahrenheit to Kelvin
Convert Fahrenheit to Celsius first, then add 273.15.
K = (°F - 32) × 5 ÷ 9 + 273.15
32 °F to Kelvin
(32 – 32) × 5 ÷ 9 + 273.15 = 273.15 K
How to Convert Kelvin to Fahrenheit
Convert Kelvin to Celsius first, then apply the Celsius to Fahrenheit formula.
°F = (K - 273.15) × 9 ÷ 5 + 32
Common Temperature Conversion Chart
| Reference | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | -273.15 °C | -459.67 °F | 0 K |
| Water freezes | 0 °C | 32 °F | 273.15 K |
| Room temperature | 20 °C | 68 °F | 293.15 K |
| Body temperature | 37 °C | 98.6 °F | 310.15 K |
| Water boils* | 100 °C | 212 °F | 373.15 K |
*The boiling point shown is for pure water at standard atmospheric pressure.
Celsius vs Fahrenheit vs Kelvin
Celsius is widely used for weather, daily temperatures, and scientific work. Fahrenheit is common in the United States for everyday temperature reporting. Kelvin is the SI base unit of thermodynamic temperature and is widely used in scientific calculations.
Celsius and Kelvin use the same interval size. Fahrenheit uses a different interval size and a different zero point.
What Is Absolute Zero?
Absolute zero is the lowest possible thermodynamic temperature. It is defined as 0 K, which equals -273.15 °C and -459.67 °F.
Why -40 °C Equals -40 °F
Celsius and Fahrenheit use different scale sizes and different zero points, but their values cross at -40.
(-40 × 9 ÷ 5) + 32 = -40 °F
This is the only temperature where the Celsius and Fahrenheit numbers are identical.
Common Temperature Conversion Mistakes
- Forgetting the 32-degree offset. Celsius and Fahrenheit are not converted by multiplication alone.
- Writing a degree symbol with Kelvin. Kelvin is written as K, not °K.
- Allowing negative Kelvin values. Kelvin cannot be below 0 K.
- Using temperature-change math for absolute temperature. A temperature difference is not converted in exactly the same way as an absolute reading.
- Rounding too early. Keep full precision during the calculation and round the displayed result at the end.
Temperature Converter FAQs
What scales does this temperature converter support?
It supports Celsius, Fahrenheit, and Kelvin.
How do I convert Celsius to Fahrenheit?
Multiply Celsius by 9/5, then add 32.
How do I convert Fahrenheit to Celsius?
Subtract 32 from Fahrenheit, then multiply by 5/9.
What is 0 °C in Fahrenheit?
0 °C equals 32 °F.
What is 100 °C in Fahrenheit?
100 °C equals 212 °F.
Can Kelvin be negative?
No. The Kelvin scale starts at absolute zero, which is 0 K.
At what temperature are Celsius and Fahrenheit equal?
Celsius and Fahrenheit have the same numeric value at -40 degrees.
Sources and Calculation Methodology
Conversion formulas reviewed September 13, 2026.
The calculator converts values through Celsius internally. Fahrenheit calculations use the standard 9/5 scale relationship and 32-degree offset. Kelvin calculations use the 273.15 offset from Celsius.
- BIPM: SI Base Unit, Kelvin
- BIPM: International System of Units
- NIST: SI Units, Temperature
- NIST: Temperature Conversion Guidance
For other measurement types, use the Length Converter, Weight Converter, or Volume Converter.