# How do I convert kelvin to Celsius?

Converts kelvins (K) to degrees Celsius (°C) and back, with the exact unit definitions.

- Page: https://www.acalculator.org/convert/kelvin-to-celsius
- JSON spec: https://www.acalculator.org/convert/kelvin-to-celsius.json
- Version: 6ed282004745

## Default answer

Example with the default inputs (Kelvins (K) 300): 300 K = 26.85 °C.

## Inputs

| Key | Label | Description |
| --- | --- | --- |
| value | Kelvins (K) | The amount in kelvins to convert. |
| result | Degrees Celsius (°C) | The same amount in degrees Celsius. |

## Outputs

| Key | Label | Description |
| --- | --- | --- |
| value | Kelvins (K) | The amount in kelvins to convert. |
| result | Degrees Celsius (°C) | The amount in degrees Celsius. |

## Method

°C = K − 273.15

## Assumptions

- A kelvin and a degree Celsius are the same size; the scales differ only in their zero: 0 K is −273.15 °C.
- Nothing is colder than absolute zero (0 K, −273.15 °C, −459.67 °F), so a value below it gives no answer.
- Exact on the typed decimals: at most 6 decimal places (6 significant digits below 0.0001), rounded half up; an answer of 1 billion or more shows at most 15 significant digits.

## Worked examples

1. value = 0 gives result = -273.15. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
2. value = 300 gives result = 26.85. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.
3. result = 26.85 gives value = 300. Source: Exact unit definitions in NIST SP 811 (2008), Appendix B.8.

## FAQ

### What is the formula to convert kelvin to Celsius?

°C = K − 273.15. For example, 300 K is 26.85 °C.

### How do I convert kelvin to Celsius?

Use °C = K − 273.15. 300 K gives 26.85 °C.

### How do I convert Celsius back to kelvin?

Reverse the formula, or type the degrees Celsius into the second box and the converter works it out.

### What is absolute zero?

0 K, the coldest possible temperature: −273.15 °C, or −459.67 °F. The kelvin scale starts there, so a temperature in kelvin is never negative, and the converter gives no answer below it.

### Is it "degrees kelvin"?

No. The unit is the kelvin, written with the symbol K and no degree sign, as in 300 K; NIST SP 811 writes T0 = 273.15 K. Celsius keeps the degree sign: 26.85 °C.

## Sources

- NIST SP 811 (2008), Chapter 4, section 4.2.1.1: Celsius temperature t = T − T0 with T0 = 273.15 K; the degree Celsius is equal in size to the kelvin, retrieved 2026-10-18. https://www.nist.gov/pml/special-publication-811/nist-guide-si-chapter-4-two-classes-si-units-and-si-prefixes
- NIST SP 811 (2008), Guide for the Use of the International System of Units, Appendix B.8: Factors for Units Listed Alphabetically (bold factors are exact), retrieved 2026-10-18. https://www.nist.gov/pml/special-publication-811/nist-guide-si-appendix-b-conversion-factors/nist-guide-si-appendix-b8