Temperature Converter
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Converting between Celsius, Fahrenheit, and Kelvin
Three temperature scales dominate everyday and scientific life, and they disagree on both their zero point and their step size. Celsius pins 0° to water freezing and 100° to it boiling. Fahrenheit places those same points at 32° and 212°, with smaller degrees. Kelvin keeps Celsius-sized degrees but starts at absolute zero, the coldest anything can be. This tool converts a number in any one scale into the other two instantly.
The formulas
- Celsius to Fahrenheit: F = C × 9/5 + 32
- Fahrenheit to Celsius: C = (F − 32) × 5/9
- Celsius to Kelvin: K = C + 273.15
- Kelvin to Celsius: C = K − 273.15
The 9/5 factor is the ratio of the scales' step sizes; the +32 and +273.15 shift the zero points. Because Fahrenheit degrees are smaller, one Celsius degree of change always equals 1.8 Fahrenheit degrees.
Reference points across all three scales
| Reference | °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 |
One curiosity: −40 is the single point where Celsius and Fahrenheit read the same number, because that is where the two lines cross.
Which scale is used where
Celsius is the everyday standard across most of the world and in cooking and weather outside the United States, which keeps Fahrenheit for daily use. Kelvin is the scientific choice because it starts at absolute zero, so quantities that depend on absolute temperature — the gas laws, thermal radiation — need Kelvin rather than Celsius. A handy mental shortcut for Celsius to Fahrenheit is "double it and add 30": 20 °C gives roughly 70 °F, where the exact answer is 68 — close enough for weather. For anything precise, use the full ×9/5 + 32, which is what this tool applies, along with the exact 273.15 offset for Kelvin.
Common mistakes
- Order of operations: for C to F you must multiply by 9/5 before adding 32. Adding first gives a wrong, colder answer.
- Rounding the Kelvin offset: it is 273.15, not 273. The 0.15 matters in scientific work and for exact freezing points.
- Writing "°K": Kelvin takes no degree symbol — it is 310 K, not 310 °K.
- Sign slips below zero: −20 °C is −4 °F, not a positive number; keep the minus through the whole calculation.
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Sources & further reading
Frequently asked questions
How do I convert Celsius to Fahrenheit in my head?
The exact formula is °F = °C × 9/5 + 32. For a quick mental estimate use "double it and add 30" (°C × 2 + 30). At everyday temperatures the shortcut is close — 20 °C gives 70 vs the exact 68 °F — but the error grows as you move away from 10-20 °C, reaching about 6 °F near boiling. For cooking or fever checks, use the exact converter above rather than the approximation.
What is 350°F in Celsius?
350 °F is about 176.7 °C, which most ovens round to 175 °C or 180 °C — the classic "moderate oven" for cakes and roasts. Other common US baking temperatures: 325 °F ≈ 160 °C, 375 °F ≈ 190 °C, 400 °F ≈ 200 °C and 425 °F ≈ 220 °C. Type 350 into the Fahrenheit box above to see the exact Celsius and Kelvin values.
Why does Kelvin have no degree (°) symbol?
Kelvin is an absolute thermodynamic unit, not a scale of "degrees" measured from an arbitrary point. Since the 1967 SI redefinition, temperatures are written as "300 K", not "300 °K". Each kelvin is exactly the same size as one degree Celsius, so the two scales differ only by an offset of 273.15.
What is absolute zero?
Absolute zero is the lowest temperature possible: −273.15 °C, −459.67 °F, or 0 K. At that point molecular motion reaches its theoretical minimum, so nothing can get colder. This converter shows values below absolute zero for reference but flags them with a warning, because no real substance can actually reach such a temperature.
Are the numbers I enter sent to a server?
No. This temperature converter runs entirely in your browser using plain JavaScript — every Celsius, Fahrenheit and Kelvin calculation happens on your device. Nothing you type is uploaded, stored or tracked, and the tool keeps working offline once the page has loaded.