Temperature Converter
Convert temperatures between Celsius, Fahrenheit, Kelvin and Rankine with the exact formula for every pair of scales.
Temperature Converter — input your values
What does this conversion calculator do?
The temperature converter works with the four most common temperature scales: Celsius, Fahrenheit, Kelvin and Rankine. It converts in both directions and always shows the exact pair formula used, such as °F = (°C × 9/5) + 32.
All conversions pass through Celsius as the reference scale. Because the scales have different zero points, the converter applies both a slope factor and an offset, which is what makes Fahrenheit to Celsius (or Kelvin) more than a simple multiplication.
Formula and variables
Water freezes at 0 °C = 32 °F = 273.15 K and boils at 100 °C = 212 °F = 373.15 K.
| Symbol | Meaning |
|---|---|
| factor(from) | How many Celsius degrees one degree of the 'from' scale equals |
| offset(from) | Celsius value of zero on the 'from' scale |
| offset(to) | Celsius value of zero on the 'to' scale |
Worked example
Convert 68 degrees Fahrenheit to Celsius.
- 68 − 32 = 36.
- 36 × 5/9 = 20.
Answer: 68 °F = 20 °C.
Tips and common mistakes
Tips
- For quick mental math: °C × 1.8 + 32 ≈ °F, and (°F − 32) ÷ 1.8 ≈ °C.
- Useful anchors: 0 °C = 32 °F (freezing), 20 °C = 68 °F (room temperature), 37 °C = 98.6 °F (body temperature), 100 °C = 212 °F (boiling).
- Kelvin has no degree symbol and never uses negative values — absolute zero is 0 K.
- When reporting weather or science data, always state which scale you used.
Common mistakes to avoid
- Adding or subtracting 32 before multiplying — the correct order is subtract 32, then multiply by 5/9 for °F → °C.
- Writing negative Kelvin values: temperatures cannot go below absolute zero (0 K = −273.15 °C).
- Using °C → K as multiply by 1.8: the Celsius to Kelvin conversion is simply adding 273.15, not multiplying.
Temperature Converter — frequently asked questions
How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, 68 °F: (68 − 32) × 5/9 = 20 °C.
What is absolute zero?
Absolute zero is 0 K = −273.15 °C = −459.67 °F, the theoretical lowest possible temperature where molecular motion stops.
At what temperature are Celsius and Fahrenheit the same?
At −40 degrees: −40 °C = −40 °F. This is a popular trick question and a genuinely handy conversion anchor.
Why does the US use Fahrenheit?
Historically the US adopted the Fahrenheit scale before the metric system spread. Celsius is the international standard (SI) used by virtually all other countries and in science.
What is the Rankine scale?
Rankine is an absolute temperature scale used mainly in American engineering. It uses Fahrenheit-sized degrees: °R = (°C + 273.15) × 9/5, and absolute zero is 0 °R.
How do I convert Celsius to Kelvin?
Simply add 273.15. For example, 25 °C = 298.15 K. Kelvin is the SI base unit of temperature.