Convert Fahrenheit to Kelvin
Convert Fahrenheit to Kelvin with the exact (°F − 32) × 5/9 + 273.15 formula. Perfect for science, engineering, and HVAC.
How to Convert Fahrenheit to Kelvin
To convert Fahrenheit to Kelvin, subtract 32, multiply by 5/9, then add 273.15.
Conversion Formula:
((value - 32) * 5/9) + 273.15Understanding the Conversion
Fahrenheit to Kelvin converts everyday Fahrenheit readings into the absolute scale required for scientific and engineering equations. The conversion adjusts both the degree size and the zero point: first remove the 32-degree offset, resize the degrees by 5/9, then shift the result upward by 273.15 to align with absolute zero.
The formula is K = (°F − 32) × 5/9 + 273.15. For example, 32°F becomes 273.15 K, 68°F becomes 293.15 K, and 451°F (a hot oven) becomes about 505.37 K. Because Kelvin cannot be negative, even subzero Fahrenheit readings transform into positive absolute temperatures.
Use this conversion for thermodynamics, combustion analysis, refrigeration design, or lab experiments when source data or specifications are expressed in Fahrenheit. The converter ensures precision, so you can plug the Kelvin value directly into formulas like the ideal gas law, Clausius–Clapeyron, or efficiency calculations without manual rounding mistakes.
For a quick approximation, convert Fahrenheit to Celsius first, then add 273. The calculator applies the exact constants automatically for accurate results.
Conversion Examples
Example: Convert 68°F to Kelvin
- Step 1: 68 − 32 = 36.
- Step 2: 36 × 5/9 = 20.
- Step 3: 20 + 273.15 = 293.15 K.
68°F = 293.15 K
Room temperature in Kelvin for physics and chemistry calculations.
Example: Convert -40°F to Kelvin
- Step 1: -40 − 32 = -72.
- Step 2: -72 × 5/9 = -40.
- Step 3: -40 + 273.15 = 233.15 K.
-40°F = 233.15 K
Shows how extreme cold Fahrenheit values remain positive on the absolute scale.
Example: Convert 451°F to Kelvin
- Step 1: 451 − 32 = 419.
- Step 2: 419 × 5/9 ≈ 232.78.
- Step 3: 232.78 + 273.15 ≈ 505.93 K.
451°F ≈ 505.93 K
Useful for high-temperature material or combustion studies expressed in Fahrenheit.
Conversion Formula
Fahrenheit degrees are smaller and offset from absolute zero. Subtract 32 to align with Celsius, scale by 5/9 to match the larger degree size, then add 273.15 to shift to the absolute Kelvin baseline.
Conversion Chart
| Fahrenheit | Kelvin |
|---|---|
| -40 | 233.15 |
| 0 | 255.37 |
| 32 | 273.15 |
| 68 | 293.15 |
| 77 | 298.15 |
| 86 | 303.15 |
| 98.6 | 310.15 |
| 122 | 323.15 |
| 212 | 373.15 |
| 451 | 505.93 |
Quick Conversion Tip
Convert to Celsius first, then add 273.15. The calculator combines both steps automatically.
Unit Definitions
Fahrenheit (°F)
Imperial temperature scale with 32°F at water freezing and 212°F at boiling.
Convert to Kelvin by first reaching Celsius with (°F − 32) × 5/9, then adding 273.15. To Rankine, simply add 459.67.
Kelvin (K)
Absolute temperature scale beginning at absolute zero, widely used in science.
To Celsius, subtract 273.15. To Fahrenheit, use (K − 273.15) × 9/5 + 32. To Rankine, multiply Kelvin by 9/5.
Common Use Cases
- Thermodynamics calculations requiring absolute temperatures.
- Combustion and engine testing when gauges report Fahrenheit.
- HVAC and refrigeration models that expect Kelvin inputs.
- Laboratory work where Fahrenheit instruments need Kelvin output.
- Academic problems converting U.S. data to SI-based equations.
- Quality control for industrial processes specified in Fahrenheit but modeled in Kelvin.
Frequently Asked Questions
Why add 273.15 after scaling?
273.15 is the Kelvin offset from Celsius. Once the Fahrenheit value is converted to Celsius, adding 273.15 moves it to the absolute scale.
Can Kelvin ever be negative after conversion?
No. Even very low Fahrenheit values convert to positive Kelvin numbers because Kelvin starts at absolute zero.
Is the multiplier 5/9 exact?
Yes. There are exactly 180 Fahrenheit degrees between freezing and boiling versus 100 Celsius degrees, giving an exact 5/9 ratio.