# Temperature conversion calculator

Converts a temperature between Celsius, Fahrenheit, kelvins, and Rankine, with the formula for each pair.

- Page: https://www.acalculator.org/convert/temperature
- JSON spec: https://www.acalculator.org/convert/temperature.json
- Version: 0c0aa3e8fd3b

## Default answer

Example with the default inputs (Temperature 68, From Fahrenheit (°F), To Celsius (°C)): 68 Fahrenheit (°F) = 20 Celsius (°C).

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| amount | Temperature | The temperature to convert, on the "From" scale. It may be negative. |
| from | From | The scale the temperature is on. |
| to | To | The scale to convert to. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| result | Converted temperature | The temperature on the "To" scale. |
| celsius | Celsius (°C) | The temperature in degrees Celsius. |
| fahrenheit | Fahrenheit (°F) | The temperature in degrees Fahrenheit. |
| kelvin | Kelvins (K) | The temperature in kelvins, above absolute zero. |
| rankine | Rankine (°R) | The temperature in degrees Rankine, Fahrenheit-sized degrees above absolute zero. |
| formula | Formula | The formula from the "From" scale to the "To" scale. |

## Method

kelvins = (t + offset) × scale for the "From" scale, then back out on the "To" scale

## Assumptions

- °C = K − 273.15 and °F = K × 9 ÷ 5 − 459.67 (NIST SP 811). Rankine is kelvins × 9 ÷ 5: Fahrenheit-sized degrees from absolute zero.
- The arithmetic is exact on the decimal you type; each answer is rounded once, and the page shows at most 6 decimal places.
- A temperature below absolute zero (0 K) has no answer.

## Worked examples

1. amount = 68, from = F, to = C gives result = 20, kelvin = 293.15, rankine = 527.67, formula = °C = (°F − 32) × 5 ÷ 9. Source: NIST SP 811 (2008), section 4.2.1.1 and Appendix B.8: (68 − 32) × 5 ÷ 9 = 20 °C.
2. amount = 100, from = C, to = F gives result = 212, kelvin = 373.15, rankine = 671.67. Source: NIST SP 811 (2008), section 4.2.1.1: 100 × 9 ÷ 5 + 32 = 212 °F.
3. amount = 98.6, from = F, to = C gives result = 37, celsius = 37, kelvin = 310.15. Source: NIST SP 811 (2008), Appendix B.8: (98.6 − 32) × 5 ÷ 9 = 37 exactly.
4. amount = -40, from = C, to = F gives result = -40, kelvin = 233.15. Source: NIST SP 811 (2008), section 4.2.1.1: −40 × 9 ÷ 5 + 32 = −40.
5. amount = 0, from = K, to = F gives result = -459.67, celsius = -273.15, rankine = 0. Source: NIST SP 811 (2008), Appendix B.8: 0 K = −273.15 °C = −459.67 °F.
6. amount = 500, from = R, to = K gives result = 277.777778, fahrenheit = 40.33. Source: NIST SP 811 (2008), Appendix B.8: K = °R × 5 ÷ 9 = 2,500 ÷ 9.

## FAQ

### How do I convert Fahrenheit to Celsius?

Subtract 32, then multiply by 5 and divide by 9. For example, 68 °F is (68 − 32) × 5 ÷ 9 = 20 °C.

### How do I convert Celsius to Fahrenheit?

Multiply by 9, divide by 5, then add 32. For example, 100 °C is 100 × 9 ÷ 5 + 32 = 212 °F, the boiling point of water at sea level.

### How do I convert Celsius to kelvins?

Add 273.15. A kelvin is the same size as a degree Celsius, and 0 K is absolute zero, −273.15 °C. So 20 °C is 293.15 K.

### At what temperature are Celsius and Fahrenheit the same?

At −40. Put −40 into °F = °C × 9 ÷ 5 + 32 and you get −72 + 32 = −40.

### What is the Rankine scale?

Rankine counts Fahrenheit-sized degrees from absolute zero, the way kelvins count Celsius-sized degrees. °R = °F + 459.67, and °R = K × 9 ÷ 5. Some US engineering tables use it.

### Why can I not enter a temperature below absolute zero?

Absolute zero (0 K, −273.15 °C, −459.67 °F, 0 °R) is the lowest temperature there is. A colder value has no answer, so the page says so instead of converting it.

### Is normal body temperature 37 °C exactly 98.6 °F?

Yes, as a conversion. 37 × 9 ÷ 5 + 32 = 98.6 exactly. The converter keeps the arithmetic exact, so 98.6 °F gives 37 °C, not 36.99999.

## Sources

- NIST SP 811 (2008), Guide for the Use of the International System of Units, section 4.2.1.1 (Celsius temperature) and Appendix B.8 (degree Fahrenheit, degree Rankine), retrieved 2026-10-01. https://www.nist.gov/pml/special-publication-811