40 degrees Fahrenheit is equal to 277.59 kelvin.
To convert Fahrenheit to Kelvin, first convert the Fahrenheit value to Celsius, and then add 273.15 to get the temperature in kelvin. This process ensures the temperature is expressed on the absolute thermodynamic scale.
Conversion Tool
Result in kelvin:
Conversion Formula
The formula to convert Fahrenheit (°F) to Kelvin (K) involves two steps. First, you convert Fahrenheit to Celsius using the formula C = (F - 32) × 5/9. Then, you convert Celsius to kelvin by adding 273.15, because kelvin is an absolute temperature scale starting at absolute zero.
In a single formula, it looks like this:
K = (F - 32) × 5/9 + 273.15
This formula works because Fahrenheit and Celsius scales are offset and scaled differently. The 32 subtracts the freezing point of water in Fahrenheit, the 5/9 scales the difference to Celsius degrees, and 273.15 shifts Celsius to kelvin.
Example: Convert 40°F to kelvin.
- Subtract 32 from 40: 40 – 32 = 8
- Multiply by 5/9: 8 × 5/9 = 4.4444
- Add 273.15: 4.4444 + 273.15 = 277.5944 K
Conversion Example
Convert 68 Fahrenheit to kelvin step-by-step:
- Start with the Fahrenheit value: 68°F
- Subtract 32: 68 – 32 = 36
- Multiply by 5/9: 36 × 5/9 = 20
- Add 273.15: 20 + 273.15 = 293.15 K
- Therefore, 68°F equals 293.15 kelvin.
Convert 0 Fahrenheit to kelvin:
- 0 – 32 = -32
- -32 × 5/9 = -17.7778
- -17.7778 + 273.15 = 255.3722 K
Convert 100 Fahrenheit to kelvin:
- 100 – 32 = 68
- 68 × 5/9 = 37.7778
- 37.7778 + 273.15 = 310.9278 K
Conversion Chart
| Fahrenheit (°F) | Kelvin (K) |
|---|---|
| 15.0 | 263.706 |
| 20.0 | 266.483 |
| 25.0 | 269.261 |
| 30.0 | 272.039 |
| 35.0 | 274.817 |
| 40.0 | 277.594 |
| 45.0 | 280.372 |
| 50.0 | 283.150 |
| 55.0 | 285.928 |
| 60.0 | 288.706 |
| 65.0 | 291.483 |
This chart shows how fahrenheit temperatures between 15.0 and 65.0 convert to kelvin. To use, find the fahrenheit number you want in the first column and read across to find its kelvin equivalent in the second column.
Related Conversion Questions
- What is 40 degrees Fahrenheit in kelvin temperature?
- How do I convert 40°F to kelvin easily?
- Is 40°F above or below freezing point in kelvin?
- What formula to use for changing 40 Fahrenheit into kelvin?
- Can 40 degrees Fahrenheit be expressed directly in kelvin?
- How much kelvin equals 40 degrees Fahrenheit exactly?
- Why does 40 Fahrenheit convert to around 277 kelvin?
Conversion Definitions
Fahrenheit: Fahrenheit is a temperature scale where water freezes at 32 degrees and boils at 212 degrees under standard atmospheric pressure. It is mostly used in the United States and some Caribbean countries. The scale was proposed by Daniel Gabriel Fahrenheit in the early 18th century.
Kelvin: Kelvin is the SI unit for temperature measurement based on absolute zero, the lowest possible temperature where particles have minimum thermal motion. It uses the same increment size as Celsius but starts at -273.15°C. Kelvin is important in scientific contexts.
Conversion FAQs
Why do we add 273.15 when converting Celsius to kelvin?
Kelvin scale starts at absolute zero, which is -273.15°C. Adding 273.15 shifts the zero point from Celsius’s freezing point of water to absolute zero, allowing temperatures to be expressed without negative numbers in scientific measurements.
Can I convert Fahrenheit directly to kelvin without going through Celsius?
Yes, the formula K = (F - 32) × 5/9 + 273.15 converts Fahrenheit directly to kelvin, combining the steps of converting to Celsius first then adding 273.15. This formula is a shortcut that avoids intermediate conversions.
What happens if I input a negative Fahrenheit value in the conversion tool?
Negative Fahrenheit values represent temperatures below freezing. The conversion formula still applies the same way, resulting in kelvin values above zero because kelvin cannot be negative. The tool calculates kelvin accordingly, even for negative Fahrenheit.
Is kelvin used outside scientific fields?
Kelvin is mostly used in science and engineering where absolute temperature measurements are needed. Everyday temperature readings use Celsius or Fahrenheit more. However, kelvin is crucial for understanding physical phenomena like gas laws and thermal dynamics.
Why is the Fahrenheit scale offset by 32 degrees?
The 32-degree offset in Fahrenheit comes from setting the freezing point of water at 32°F. It was designed so that human body temperature was near 100°F and the scale covers common weather temperatures conveniently. This offset requires adjustment when converting to other scales.