Temperature Converter
Convert Celsius, Fahrenheit, and Kelvin with the exact formulas and key reference points.
What it does
Three scales share the same heat with different zeroes. Celsius sets 0 at the freezing point of water and 100 at the boiling point at sea level. Fahrenheit shifts both numbers, and Kelvin starts at absolute zero, the point where classical thermal motion stops.
The tool above converts any one scale into all three at once. Enter the value, pick its scale, and read the rest. Values below absolute zero are rejected, since they cannot exist.
Spacing matters for weather sense. One Celsius degree equals 1.8 Fahrenheit degrees, so a 10 C swing feels like an 18 F swing. Kelvin degrees match Celsius degrees in size and differ only by the 273.15 offset.
How to use
- Enter the temperature number.
- Pick the scale it is written in.
- Read all three results. No second step is needed.
- For cooking and weather, round to whole degrees. For science, keep one or two decimals.
Formula
- 32
- Offset aligning the different zeroes.
- 9/5, 5/9
- Degree size ratio between the scales.
- 273.15
- Celsius to Kelvin shift. Kelvin starts at absolute zero.
Convert to Celsius first, then out to the wanted scale. The 32 aligns the different zeroes and the 9/5 stretches the degree size. Kelvin never takes a degree sign, only the number plus K.
Worked example
Example: 68 F to Celsius and Kelvin
Room temperature of 68 Fahrenheit, converted both ways.
- Subtract the offset: 68 - 32 = 36.
- Scale the size: 36 x 5/9 = 20 C.
- Shift to Kelvin: 20.0 + 273.15 = 293.15 K.
- Result: 68 F = 20 C = 293.15 K.
Reference table
| Point | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Room temperature | 20 | 68 | 293.15 |
| Water boils (sea level) | 100 | 212 | 373.15 |
Limits
- Nothing exists below minus 273.15 C.
- Boiling shifts with altitude and pressure.
- Body temperature varies by person and time of day.
- Historic scales like Rankine sit outside this page.
Common mistakes
- Forgetting the 32 offset and scaling only, which wrecks Fahrenheit results.
- Flipping 5/9 with 9/5 on the way back.
- Writing Kelvin with a degree sign. The unit is simply K.
- Expecting boiling at 100 C high in the mountains, where lower pressure drops it.
- Rounding the offset before scaling on precise lab numbers.
Try it yourself
Quick checks. Answers sit tucked under each question.
0 C in Fahrenheit?
0 x 9/5 + 32 = 32 F.
Which reads minus 40 on both?
Minus 40 C equals minus 40 F, the single crossover.
Questions
What is 20 C in Fahrenheit?
68 F. Multiply 20 by 9/5 to get 36, then add 32.
What is minus 40?
The crossover: minus 40 C equals minus 40 F, the one point where both scales agree.
When do I use Kelvin?
For science and gas law math, where ratios need a true zero. Weather and cooking stay in Celsius or Fahrenheit.
Can temperature go below absolute zero?
No. Minus 273.15 C is the floor in current physics, and the tool rejects anything lower.
Why does the US use Fahrenheit?
History and habit. Its finer degrees suit weather talk, while science worldwide uses Celsius and Kelvin.