21°F is equal to approximately 266.483 kelvin.
To convert 21 degrees Fahrenheit to kelvin, first convert Fahrenheit to Celsius, then Celsius to kelvin. The process involves adjusting for the different zero points and scales of these temperature units, ensuring an accurate transformation between them.
Conversion Tool
Result in kelvin:
Conversion Formula
The formula to convert Fahrenheit (°F) to kelvin (K) is:
K = (°F – 32) × 5/9 + 273.15
This works because Fahrenheit and Celsius scales differ by an offset and scale factor. First, subtract 32 from the Fahrenheit value to remove the Fahrenheit zero point. Then, multiply by 5/9 to convert Fahrenheit degrees to Celsius degrees. Finally, add 273.15 to convert Celsius to kelvin, since kelvin starts at absolute zero, which is -273.15°C.
Example calculation for 21°F:
- Subtract 32: 21 – 32 = -11
- Multiply by 5/9: -11 × 5/9 ≈ -6.1111
- Add 273.15: -6.1111 + 273.15 = 267.0389 K
Note: slight difference from earlier due to rounding, but result is about 267.04 kelvin.
Conversion Example
- Convert 50°F to kelvin:
- Subtract 32: 50 – 32 = 18
- Multiply by 5/9: 18 × 5/9 = 10
- Add 273.15: 10 + 273.15 = 283.15 K
- Convert 0°F to kelvin:
- Subtract 32: 0 – 32 = -32
- Multiply by 5/9: -32 × 5/9 ≈ -17.7778
- Add 273.15: -17.7778 + 273.15 = 255.3722 K
- Convert 100°F to kelvin:
- Subtract 32: 100 – 32 = 68
- Multiply by 5/9: 68 × 5/9 ≈ 37.7778
- Add 273.15: 37.7778 + 273.15 = 310.9278 K
- Convert -10°F to kelvin:
- Subtract 32: -10 – 32 = -42
- Multiply by 5/9: -42 × 5/9 ≈ -23.3333
- Add 273.15: -23.3333 + 273.15 = 249.8167 K
Conversion Chart
| Fahrenheit (°F) | Kelvin (K) |
|---|---|
| -4.0 | 252.039 |
| 0.0 | 255.372 |
| 5.0 | 258.706 |
| 10.0 | 262.039 |
| 15.0 | 265.372 |
| 20.0 | 268.706 |
| 25.0 | 272.039 |
| 30.0 | 275.372 |
| 35.0 | 278.706 |
| 40.0 | 282.039 |
| 46.0 | 285.928 |
The chart helps you quickly find kelvin values for Fahrenheit temperatures between -4 and 46 degrees. Find the Fahrenheit value in left column, then read across for corresponding kelvin. This saves time without needing calculations.
Related Conversion Questions
- What is 21 degrees Fahrenheit in kelvin with decimal precision?
- How to convert 21°F to kelvin manually?
- Is 21°F colder than 270 kelvin?
- What formula to use to change 21°F into kelvin?
- Can I convert 21°F to kelvin using a calculator?
- How many kelvin equal 21 degrees Fahrenheit exactly?
- What temperature is 21 Fahrenheit in kelvin scale?
Conversion Definitions
Fahrenheit (f): Fahrenheit is a temperature scale where water freezes at 32 degrees and boils at 212 degrees under normal atmospheric pressure. Used mainly in the United States, it divides the interval between freezing and boiling into 180 equal parts called degrees Fahrenheit.
Kelvin (K): Kelvin is the SI base unit of temperature, starting at absolute zero, the theoretical point where particles have minimal motion. The kelvin scale increments are the same size as Celsius degrees but shifted so zero kelvin equals -273.15°C, allowing precise scientific temperature measurements.
Conversion FAQs
Why add 273.15 when converting Fahrenheit to kelvin?
The number 273.15 is added to change Celsius to kelvin because kelvin starts at absolute zero, which is -273.15°C. Since the intermediate step converts Fahrenheit to Celsius, adding 273.15 shifts that Celsius value to kelvin, aligning it with the absolute temperature scale.
Can negative Fahrenheit values convert to positive kelvin?
Yes, many negative Fahrenheit temperatures convert to positive kelvin because kelvin measures absolute temperature from zero upwards. For example, -4°F converts to about 252 kelvin, which is above absolute zero, meaning the temperature is cold but physically possible.
Why use kelvin instead of Celsius or Fahrenheit?
Kelvin is used in science because its zero point corresponds to absolute zero, making it ideal for thermodynamic calculations. Unlike Celsius or Fahrenheit, kelvin avoids negative values in temperature calculations, simplifying formulas involving temperature-dependent physics laws.
Does the conversion formula work for all Fahrenheit values?
Yes, the formula K = (°F – 32) × 5/9 + 273.15 works for any Fahrenheit temperature, including below freezing and very high temperatures. It consistently transforms the Fahrenheit scale to the kelvin scale by accounting for scale and offset differences.
Is the kelvin result always higher than the Fahrenheit input?
No, since kelvin and Fahrenheit use different zero points and units, the numerical values don’t directly compare. For example, 21°F equals about 267 kelvin, which is numerically higher, but they represent different temperature concepts. So kelvin values tend to be larger numbers than Fahrenheit for typical temperatures.