Temperature Conversion Formulas and Reference Guide
A temperature converter changes a value between Celsius, Fahrenheit, Kelvin, and Rankine using fixed mathematical relationships between the scales. Enter a value in the converter above to calculate all four equivalents at the same time.
Temperature Conversion Formulas
Celsius and Kelvin use equal-sized intervals but different zero points. Fahrenheit and Rankine also use equal-sized intervals, while their interval size differs from Celsius and Kelvin.
| From | To | Formula |
|---|---|---|
| Celsius | Fahrenheit | °F = °C × 9/5 + 32 |
| Fahrenheit | Celsius | °C = (°F − 32) × 5/9 |
| Celsius | Kelvin | K = °C + 273.15 |
| Kelvin | Celsius | °C = K − 273.15 |
| Fahrenheit | Kelvin | K = (°F − 32) × 5/9 + 273.15 |
| Kelvin | Fahrenheit | °F = (K − 273.15) × 9/5 + 32 |
| Celsius | Rankine | °R = (°C + 273.15) × 9/5 |
| Rankine | Celsius | °C = °R × 5/9 − 273.15 |
Common Temperature Conversion Chart
| Celsius (°C) | Fahrenheit (°F) | Kelvin (K) | Rankine (°R) | Reference |
|---|---|---|---|---|
| −273.15 | −459.67 | 0 | 0 | Absolute zero |
| −40 | −40 | 233.15 | 419.67 | Celsius and Fahrenheit are equal |
| 0 | 32 | 273.15 | 491.67 | Water freezing reference at standard pressure |
| 20 | 68 | 293.15 | 527.67 | Typical room temperature |
| 25 | 77 | 298.15 | 536.67 | Common laboratory reference |
| 37 | 98.6 | 310.15 | 558.27 | Approximate human body temperature |
| 100 | 212 | 373.15 | 671.67 | Water boiling reference at standard pressure |
| 176.67 | 350 | 449.82 | 809.67 | Common oven setting |
Understanding Celsius, Fahrenheit, Kelvin, and Rankine
Celsius
Celsius is widely used for weather, cooking, education, and laboratory reporting. Its unit symbol is °C. The Celsius interval is the same size as the kelvin interval.
Fahrenheit
Fahrenheit is commonly used for weather and everyday temperature reporting in the United States. Water freezes at 32°F and boils at 212°F under standard reference conditions.
Kelvin
Kelvin is the SI unit of thermodynamic temperature. It is written as K without a degree symbol. For ordinary absolute-temperature conversion, values cannot be below 0 K.
Rankine
Rankine is an absolute temperature scale that uses Fahrenheit-sized intervals. Absolute zero is 0°R, and a temperature difference of 1°R equals a difference of 1°F.
Absolute Temperature vs Temperature Difference
Converting an absolute temperature is different from converting a temperature difference. Absolute conversions use scale offsets, while temperature differences use only interval ratios.
- A difference of 1 K equals a difference of 1°C.
- A difference of 1°C equals a difference of 1.8°F.
- A difference of 1°F equals a difference of 5/9°C.
- A difference of 1°R equals a difference of 1°F.
Worked Temperature Conversion Examples
Example 1: Convert 20°C to Fahrenheit and Kelvin
Fahrenheit: °F = 20 × 9/5 + 32 = 68°F
Kelvin: K = 20 + 273.15 = 293.15 K
Example 2: Convert 350°F to Celsius
°C = (350 − 32) × 5/9
°C = 318 × 5/9
350°F ≈ 176.67°C
Common Temperature Conversion Mistakes
- Using the wrong direction: Celsius-to-Fahrenheit and Fahrenheit-to-Celsius use different formulas.
- Forgetting the offset: multiplication alone is not enough for Celsius and Fahrenheit conversions.
- Using a degree symbol with Kelvin: write 300 K, not 300°K.
- Allowing values below absolute zero: Kelvin and Rankine cannot be negative in ordinary absolute-temperature conversion.
- Rounding too early: complete the calculation before applying display precision.
- Confusing values with intervals: temperature differences use different conversion rules.
How to Verify a Temperature Conversion
Convert the answer back to the original scale. For example, 20°C equals 68°F. Checking the answer gives:
°C = (68 − 32) × 5/9 = 20°C
Frequently Asked Questions
This converter supports Celsius, Fahrenheit, Kelvin, and Rankine.
Multiply Celsius by 9/5 and add 32: °F = °C × 9/5 + 32.
Subtract 32 and multiply by 5/9: °C = (°F − 32) × 5/9.
Add 273.15 to the Celsius value: K = °C + 273.15.
−40 is the same numerical temperature on both scales: −40°C = −40°F.
For ordinary thermodynamic temperature conversion, Kelvin values cannot be below 0 K.
Kelvin is an SI unit written with the symbol K, without a degree sign.
Yes. Temperature intervals use scale ratios but not the same zero-point offsets used for absolute temperature values.
Calculation Methodology
This converter uses Celsius as the internal reference scale. Each input is converted once to an unrounded Celsius value, and all outputs are calculated from that value. Rounding is applied only for display according to the selected precision.
Values below absolute zero are rejected: −273.15°C, −459.67°F, 0 K, and 0°R are the minimum accepted values for their respective scales.
Last reviewed: July 26, 2026
Explore Related Temperature Tools
For detailed pair-specific formulas, examples, and tables, use the Celsius to Fahrenheit Converter or the Kelvin to Celsius Converter . You can also browse all Conversion Calculators .
