Convert between Celsius, Fahrenheit, Kelvin, and Rankine temperature scales
Temperature is a measure of the average kinetic energy of particles in a substance. Different temperature scales were developed for various purposes, from scientific research to everyday weather reporting. Understanding how to convert between these scales is essential in science, cooking, engineering, and international communication.
The Celsius scale, used by most of the world, sets water's freezing point at 0° and boiling point at 100° at standard atmospheric pressure. The Fahrenheit scale, common in the United States, sets these at 32° and 212° respectively. Kelvin, the SI unit for temperature, starts at absolute zero—the theoretical point where all molecular motion stops.
This converter handles all major temperature scales instantly, making it easy to work with international recipes, scientific data, weather reports from different countries, or HVAC calculations that use different standards.
Metric scale based on water. Used globally for weather, cooking, and science. 0°C = freezing, 100°C = boiling.
Used in USA for weather and cooking. 32°F = freezing, 212°F = boiling. Body temp is 98.6°F.
Absolute scale for science. 0K = absolute zero (-273.15°C). No degree symbol used.
Absolute scale using Fahrenheit degrees. Used in some engineering applications. 0°R = absolute zero.
| Reference Point | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute Zero | -273.15°C | -459.67°F | 0 K |
| Water Freezes | 0°C | 32°F | 273.15 K |
| Room Temperature | 20-22°C | 68-72°F | 293-295 K |
| Body Temperature | 37°C | 98.6°F | 310.15 K |
| Water Boils | 100°C | 212°F | 373.15 K |
| Oven (Moderate) | 180°C | 350°F | 453.15 K |
Double the Celsius, then add 30 for a quick estimate. 20°C ≈ (20×2)+30 = 70°F (actual: 68°F).
-40° is the same in both Celsius and Fahrenheit—the only point where the two scales meet.
Add 273 to Celsius for Kelvin (273.15 for precision). Room temp 20°C = 293K.
0°C/32°F = coat weather, 20°C/68°F = comfortable, 30°C/86°F = hot, 40°C/104°F = heat wave.
Historical inertia and the costs of switching. Fahrenheit was established in the US before metric standardization. While science and medicine use Celsius, everyday weather and cooking still use Fahrenheit due to familiarity and infrastructure.
Absolute zero (0 K or -273.15°C) is the theoretical lowest temperature where all thermal motion stops. It's physically unattainable but crucial in physics, defining the Kelvin scale and helping scientists understand thermodynamics and quantum mechanics.
Kelvin has no negative values, making calculations simpler. Many physics equations require absolute temperature. Gas laws, thermodynamics, and radiation calculations all work more cleanly with Kelvin's absolute zero baseline.
Use the formula F = (C × 9/5) + 32. Common conversions: 180°C = 350°F (moderate oven), 200°C = 400°F (hot oven), 220°C = 425°F (very hot). Most recipes include both for convenience.
Normal core body temperature is often cited as 98.6 °F. Convert this reading to Celsius and Kelvin.
Result98.6 °F = 37 °C = 310.15 K
Apply C = (F − 32) × 5/9 = (98.6 − 32) × 5/9 = 66.6 × 5/9 = 37 °C. Then K = C + 273.15 = 37 + 273.15 = 310.15 K. The same temperature in Rankine is R = F + 459.67 = 558.27 °R.
To go from Celsius to Fahrenheit, use F = 9/5 × C + 32. To go the other way, use C = (F − 32) × 5/9. The factor 9/5 reflects that 100 Celsius degrees span the same range as 180 Fahrenheit degrees between water's freezing and boiling points at 1 atm.
Celsius is the everyday scale in nearly every country and is the standard for weather, cooking, and medicine outside the United States. Fahrenheit remains in daily use in the US and a few territories. Kelvin is the SI base unit used in science and engineering, and Rankine appears mainly in US thermodynamics and HVAC work.
Kelvin starts at absolute zero (0 K = −273.15 °C), so it never goes negative. Many physical laws — the ideal gas law, the Stefan-Boltzmann law, and most thermodynamic equations — assume an absolute temperature. Using Kelvin avoids sign errors and keeps proportional relationships (doubling K means doubling thermal energy) intuitive.
Practically yes. The scale was called centigrade ('hundred steps') until the 9th General Conference on Weights and Measures renamed it Celsius in 1948 to honor astronomer Anders Celsius and avoid confusion with the centigrade angular unit. Modern standards and SI documentation use Celsius exclusively.
Absolute zero is the theoretical lower limit of temperature, defined as 0 K, −273.15 °C, or −459.67 °F. At this point a system has minimum possible thermal energy. The third law of thermodynamics says it can be approached arbitrarily closely but never reached in a finite number of steps.
Double the Celsius value and add 30 for a rough estimate. So 20 °C becomes about 70 °F (the exact value is 68 °F). For a more accurate shortcut, double, subtract 10 percent, then add 32. The two scales meet at exactly −40°, which is the same number on both.
Rankine is an absolute scale built on the Fahrenheit degree size, the way Kelvin is built on the Celsius degree. Convert with R = F + 459.67, or directly from Kelvin with R = K × 9/5. It appears in US engineering, especially in steam tables, combustion analysis, and aerospace thermodynamics.
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