Convert temperatures between Celsius, Fahrenheit, and Kelvin with live results, step-by-step formulas, and a visual thermometer.
8 min read | ~1,600 wordsThe relationship between Celsius and Fahrenheit is linear. Both scales are offset and scaled differently because Daniel Fahrenheit originally calibrated his 1724 scale using a brine solution (0°F) and human body temperature (96°F), while Anders Celsius his 1742 scale around the freezing (0°C) and boiling (100°C) points of water at sea level.
| Description | °C | °F | K |
|---|---|---|---|
| Absolute zero | -273.15 | -459.67 | 0 |
| Dry ice sublimation | -78.5 | -109.3 | 194.65 |
| Scales equal (C = F) | -40 | -40 | 233.15 |
| Water freezes | 0 | 32 | 273.15 |
| Refrigerator | 4 | 39.2 | 277.15 |
| Cool room | 16 | 60.8 | 289.15 |
| Room temperature | 20 | 68 | 293.15 |
| Warm day | 30 | 86 | 303.15 |
| Human body | 37 | 98.6 | 310.15 |
| Hot tub | 40 | 104 | 313.15 |
| Fever threshold | 38.3 | 101 | 311.45 |
| Pasteurization | 72 | 161.6 | 345.15 |
| Water boils | 100 | 212 | 373.15 |
| Baking (moderate oven) | 180 | 356 | 453.15 |
| Baking (hot oven) | 220 | 428 | 493.15 |
| Deep frying oil | 190 | 374 | 463.15 |
| Pizza oven | 300 | 572 | 573.15 |
The Celsius and Fahrenheit scales were developed independently in the 18th century. Understanding the conversion between them comes down to two factors: the offset and the ratio.
Water freezes at 0°C but at 32°F, creating an offset of 32 degrees. A single Celsius degree represents a larger temperature change than a single Fahrenheit degree. Specifically, one Celsius degree equals 1.8 Fahrenheit degrees. This is where the 9/5 multiplier comes from.
To convert from Celsius to Fahrenheit, you first scale up by the 9/5 ratio to match the Fahrenheit degree size, then shift by adding 32 to account for the different zero point. Going the other direction, you reverse the process: remove the 32-degree offset first, then scale down by 5/9.
The Kelvin scale shares the same degree size as Celsius but starts at absolute zero (-273.15°C). Scientists prefer Kelvin because it simplifies thermodynamic calculations by eliminating negative values in most practical scenarios. To get Kelvin from Celsius, simply add 273.15.
A useful mental shortcut for approximate conversions: double the Celsius value and add 30 to estimate Fahrenheit. For example, 25°C is about (25 × 2) + 30 = 80°F. The actual answer is 77°F, so this quick method gets you close enough for everyday use.
Another tip worth knowing: each increase of 5 degrees Celsius corresponds to an increase of 9 degrees Fahrenheit. This makes it easy to adjust from known reference points. If you know that 20°C = 68°F, then 25°C = 77°F (add 9), and 30°C = 86°F (add another 9).
Enter multiple temperatures, one per line. Prefix with C, F, or K (e.g. "C 100" or "F 212"). Plain numbers are treated as Celsius.
Common conversions from -50°C to 250°C in 10-degree increments.
| °C | °F | K | Context |
|---|
Multiply the Celsius value by 9/5 (or 1.8), then add 32. F = (C × 9/5) + 32. For example, 25°C equals (25 × 1.8) + 32 = 77°F.
Subtract 32 from the Fahrenheit value, then multiply by 5/9. C = (F - 32) × 5/9. For example, 98.6°F equals (98.6 - 32) × 5/9 = 37°C.
The two scales intersect at -40 degrees. At this point, -40°C equals exactly -40°F. This is the only temperature where both scales produce the same number.
Absolute zero, the lowest possible temperature where all molecular motion stops, is -273.15°C or -459.67°F. It corresponds to 0 Kelvin on the Kelvin scale.
The United States adopted Fahrenheit because it was the dominant scale when the country was founded. Daniel Fahrenheit created the scale in 1724. While most nations later switched to Celsius as part of the metric system, the US retained Fahrenheit for everyday use, particularly in weather reporting and cooking.
The Kelvin scale is used primarily in scientific contexts. It starts at absolute zero (0 K = -273.15°C) and uses the same increment size as Celsius. Scientists prefer Kelvin because it has no negative values in most practical thermodynamic calculations, making equations simpler.
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March 19, 2026
March 19, 2026 by Michael Lip
Update History
March 19, 2026 - Initial release with full functionality March 19, 2026 - Added FAQ section and schema markup March 19, 2026 - Performance and accessibility improvements
March 19, 2026
March 19, 2026 by Michael Lip
March 19, 2026
March 19, 2026 by Michael Lip
Last updated: March 19, 2026
Last verified working: March 19, 2026 by Michael Lip