Temperature Converter
Convert between the three common temperature scales instantly.
Last updated: August 2026 · Written and verified by Akash Pandey
Convert temperature
°F
This runs the same calculation engine as the main scientific calculator, entirely in your browser. Nothing you type is sent anywhere.
Why you cannot just multiply, unlike length or weight
Converting length or weight is pure scaling: double the metres and you double the feet, because both scales start at zero in the same place (no length). Temperature scales do not share a common zero - 0°C is not "no temperature", it is an arbitrary reference point (water's freezing point), and 0°F is a different arbitrary point again. That is why the formula has both a multiplication and an addition: the multiplication rescales the size of one degree, and the addition shifts the two zero points into alignment. Kelvin is the exception - it starts at true physical zero (no molecular motion), which is why Kelvin conversions are a pure shift with no rescaling at all.
Temperature scales
| Scale | Freezing point of water | Boiling point of water |
|---|---|---|
| Celsius (°C) | 0°C | 100°C |
| Fahrenheit (°F) | 32°F | 212°F |
| Kelvin (K) | 273.15 K | 373.15 K |
Reference points
| Description | °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 |
Conversion formulas
°F = °C × 9/5 + 32
- To convert Celsius to Fahrenheit: multiply by 9/5, then add 32.
- To convert Fahrenheit to Celsius: subtract 32, then multiply by 5/9.
K = °C + 273.15
- Kelvin starts at absolute zero (−273.15°C).
- A temperature difference of 1°C = 1 K.
Real-world uses
- Cooking - a US recipe's "350°F oven" is 176.7°C, which is why European recipes and appliance dials round it to 180°C; the two are close but not identical.
- Fever - a US thermometer reading of 100.4°F is exactly 38.0°C, the threshold commonly used to define a fever.
- Weather - the same forecast is read as "warm" at 25°C and "warm" at 77°F, since they describe the same air temperature in different scales.
- Science and engineering - Kelvin is used whenever a formula needs an absolute scale, such as gas laws or radiative-heat calculations, because negative Celsius values would make those equations behave incorrectly.
Worked examples
Convert normal body temperature, 37°C, to Fahrenheit
37 × 9/5 + 32
- Given: 37°C. We want the equivalent on the Fahrenheit scale.
- Method: rescale first (×9/5), then shift the zero point (+32) - order matters, since this is an affine formula, not a simple ratio.
- Calculation:
37 × 9/5 = 66.6, then66.6 + 32 = 98.6. - Interpretation: 98.6°F is the commonly quoted "normal" reading.
= 98.6°F
A recipe calls for a 220°C oven - what does a Fahrenheit dial show?
220 × 9/5 + 32
- Given: 220°C target oven temperature.
- Method: apply the same C-to-F formula used above.
- Calculation:
220 × 9/5 = 396, then396 + 32 = 428. - Interpretation: 428°F - most US ovens will round the dial to 425°F, close enough for baking.
= 428°F
A common mistake: converting a temperature difference like a temperature
If a room warms up "by 10°C", that change converts differently from a temperature reading. A change of 10°C equals a change of 18°F (multiply by 9/5 only - there is no zero point to shift, because you are describing a gap, not a position on the scale). Plugging a temperature difference into the full formula and adding 32 is a common and easy mistake, and it produces a nonsensical answer.
Frequently Asked Questions
What is absolute zero?
Absolute zero is the lowest possible temperature: 0 K, −273.15°C, or −459.67°F. At this point, all molecular motion theoretically stops.
Why does temperature conversion need addition as well as multiplication?
Because Celsius and Fahrenheit place zero at different physical points (water freezing vs. a brine mixture Fahrenheit used historically). The multiplication rescales degree size; the addition realigns the two zero points. Kelvin needs only a shift, since it shares Celsius's degree size but starts at true physical zero instead.
When is Kelvin used instead of Celsius?
Whenever a calculation needs an absolute scale - gas laws, radiation formulas, and anything involving a ratio of temperatures - because a negative Celsius value would make those formulas give nonsensical results. Everyday weather and cooking never need it.
How do I convert Celsius to Fahrenheit quickly, without a calculator?
Double the Celsius value and add 30. For example, 20°C ≈ 2×20 + 30 = 70°F (exact: 68°F). This approximation is within about 2 degrees for typical weather temperatures, but drifts further from exact at extreme values.
At what temperature are Celsius and Fahrenheit equal?
At −40 degrees, both scales read the same: −40°C = −40°F. Solving °C × 9/5 + 32 = °C for °C gives exactly this value - the one point where the shift and the rescaling cancel out.
If it warms up by 10°C, how many degrees Fahrenheit is that?
18°F, not what the full formula gives. A change in temperature only needs the ×9/5 rescaling - there is no zero point to realign for a difference, so do not add 32 when converting a temperature change rather than a temperature reading.
Why does water boil at different temperatures in different places?
The 100°C / 212°F boiling point assumes standard atmospheric pressure (1 atm, sea level). At altitude, lower air pressure lets water boil at a lower temperature - about 93°C at 2,000 m elevation - which is why recipes sometimes give altitude adjustments.
How do I convert Fahrenheit to Celsius in my head?
Subtract 30 from the Fahrenheit value, then divide by 2. For example, 86°F ≈ (86 − 30) ÷ 2 = 28°C (exact: 30°C). This approximation is within about 2 degrees for typical weather temperatures.