# Free online Celsius to Fahrenheit calculator

> Celsius and Fahrenheit are two ways to measure temperature. This calculator converts between them (and Kelvin) instantly.

Convert temperature instantly between Celsius, Fahrenheit, and Kelvin. Includes a quick-reference table of common temperatures.

**Interactive version:** https://onlinecalculator.me/unit-converters/celsius-fahrenheit/
**Category:** Unit Converters

## How to use

1. Enter the temperature you want to convert.
2. Select the source unit (°C, °F, or K).
3. The result in all three units appears instantly.
4. Scroll down for a table of common reference temperatures.

## The formulas

**Celsius → Fahrenheit:** F = C × 9/5 + 32

**Fahrenheit → Celsius:** C = (F − 32) × 5/9

**Celsius → Kelvin:** K = C + 273.15

**Kelvin → Celsius:** C = K − 273.15

## Common reference points

| Temperature | °C | °F | K |
|---|---|---|---|
| Absolute zero | −273.15 | −459.67 | 0 |
| Water freezes | 0 | 32 | 273.15 |
| Room temperature | 20 | 68 | 293.15 |
| Body temperature | 37 | 98.6 | 310.15 |
| Water boils | 100 | 212 | 373.15 |

## Notes

- Source: NIST temperature definitions and SI unit standards.
- Results are rounded to 4 decimal places to avoid floating-point noise.
- The Kelvin scale has no negative values — temperatures below 0 K are physically impossible.

## Frequently asked questions

### How do you convert Celsius to Fahrenheit?

F = C × 9/5 + 32. Example: 100°C = 100 × 1.8 + 32 = 212°F (boiling point of water).

### How do you convert Fahrenheit to Celsius?

C = (F − 32) × 5/9. Example: 98.6°F = (98.6 − 32) × 5/9 = 37°C (normal body temperature).

### How do you convert Celsius to Kelvin?

K = C + 273.15. Kelvin uses the same scale increment as Celsius but starts at absolute zero (−273.15°C). Example: 0°C = 273.15 K.

### At what temperature are Celsius and Fahrenheit equal?

−40°. At −40°C = −40°F, the two scales intersect. This is because the offset (32) and scale factor (9/5) produce the same value at that point.

### What is absolute zero in all three scales?

Absolute zero is 0 K = −273.15°C = −459.67°F. It is the theoretical temperature at which all thermal motion ceases.

## Sources

- [Fahrenheit — temperature scale and conversion to Celsius](https://en.wikipedia.org/wiki/Fahrenheit) — Wikipedia
- [Celsius — temperature scale and conversion to Fahrenheit](https://en.wikipedia.org/wiki/Celsius) — Wikipedia

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