21 °F is equal to 266.483 kelvin.
To convert 21 degrees Fahrenheit to kelvin, first convert the temperature to Celsius by subtracting 32 and multiplying by 5/9, then add 273.15 to that result. This two-step process gets us from Fahrenheit to kelvin.
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 by first changing Fahrenheit to Celsius using (F – 32) × 5/9 because Fahrenheit and Celsius scales differ by an offset of 32 degrees and a ratio of 5 to 9. Then, adding 273.15 shifts Celsius to the kelvin scale, which starts at absolute zero.
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 rounding differences may occur based on decimal places used.
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
- So, 50 °F = 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
- So, 0 °F = 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
- So, 100 °F = 310.9278 K
Conversion Chart
| Fahrenheit (°F) | Kelvin (K) |
|---|---|
| -4.0 | 256.483 |
| 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 |
| 45.0 | 285.372 |
| 46.0 | 285.927 |
You can use the chart by finding your Fahrenheit value in the left column and reading across to find its kelvin equivalent in the right column. This is handy when you want a quick reference without calculation.
Related Conversion Questions
- What is 21 degrees Fahrenheit converted into kelvin exactly?
- How to convert 21°F temperature value to kelvin scale?
- What kelvin temperature equals 21 fahrenheit degrees?
- Is 21°F warmer or colder than 266 kelvin?
- How much is 21 F in K with decimals?
- Why does 21 °F convert to around 266 kelvin?
- What is the formula to get kelvin from 21°F?
Conversion Definitions
Fahrenheit (f): Fahrenheit is a temperature scale mainly used in the United States, where water freezes at 32 degrees and boils at 212 degrees under standard atmospheric pressure. The scale divides the interval between freezing and boiling into 180 degrees, making it different from Celsius and kelvin scales.
Kelvin (K): Kelvin is the SI base unit of temperature used in scientific contexts. It starts at absolute zero, the theoretical point where particles have minimum thermal motion. Each kelvin increment equals one degree Celsius, but kelvin scale does not use negative numbers, making it convenient for absolute temperature measurements.
Conversion FAQs
Why do we subtract 32 in the Fahrenheit to kelvin conversion?
Subtracting 32 removes the Fahrenheit freezing point offset. Fahrenheit scale sets water freezing at 32°F, so subtracting 32 aligns the value to zero at freezing, matching the Celsius scale’s zero. This is necessary before converting to kelvin since kelvin is based on the Celsius zero point.
Can the conversion formula be rearranged to convert kelvin back to Fahrenheit?
Yes, you can rearrange the formula. Starting from K = (F – 32) × 5/9 + 273.15, solving for F gives F = (K – 273.15) × 9/5 + 32. This formula converts kelvin temperature back into Fahrenheit.
Does the conversion consider atmospheric pressure or humidity?
No, the conversion formula only changes units between temperature scales and doesn’t account for environmental factors like pressure or humidity. Those can affect physical temperature behavior but not the mathematical conversion between Fahrenheit and kelvin.
Is kelvin always a higher number than Fahrenheit for the same temperature?
Not always. Kelvin starts from absolute zero (0 K), so very cold Fahrenheit temperatures below -459.67°F would correspond to zero kelvin, which is the lowest possible temperature. For common temperatures like 21°F, kelvin values are higher, but the relationship depends on the scale.
Why is kelvin used more in science than Fahrenheit?
Kelvin is absolute and has no negative values, simplifying many scientific calculations. It relates directly to particle energy and thermodynamics, while Fahrenheit is a relative scale based on water freezing and boiling points, making kelvin more suitable for precise measurements.