Temperature Converter
Our free conversions & measurement calculator solves temperature problems. Get worked examples, visual aids, and downloadable results.
Reviewed for accuracy by Manoj Kumar, Mathematics Educator
Temperature Converter
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Formula: F = C * 9/5 + 32 | K = C + 273.15
Worked example — 100 C = 212 F = 373.15 K = 671.67 R
Formula
F = C * 9/5 + 32 | K = C + 273.15
Temperature conversion requires specific formulas for each pair of scales because temperature scales have different zero points and degree sizes. Celsius and Kelvin share the same degree size but differ by 273.15. Fahrenheit uses a degree that is 5/9 the size of a Celsius degree and has its zero offset by 32 from Celsius.
Worked Examples
Example 1: Converting 100 Celsius to All Scales
Problem:Convert 100 degrees Celsius (boiling point of water) to Fahrenheit, Kelvin, Rankine, and other temperature scales.
Solution:Fahrenheit = (100 * 9/5) + 32 = 212 F Kelvin = 100 + 273.15 = 373.15 K Rankine = 373.15 * 9/5 = 671.67 R Delisle = (100 - 100) * 3/2 = 0 De Newton = 100 * 33/100 = 33 N Reaumur = 100 * 4/5 = 80 Re Romer = 100 * 21/40 + 7.5 = 60 Ro
Result:100 C = 212 F = 373.15 K = 671.67 R
Example 2: Body Temperature in All Scales
Problem:Convert normal human body temperature (98.6 F) to Celsius, Kelvin, and Rankine.
Solution:Celsius = (98.6 - 32) * 5/9 = 37 C Kelvin = 37 + 273.15 = 310.15 K Rankine = (98.6 + 459.67) = 558.27 R Delisle = (100 - 37) * 3/2 = 94.5 De
Result:98.6 F = 37 C = 310.15 K = 558.27 R
Frequently Asked Questions
How do you convert Celsius to Fahrenheit?
To convert Celsius to Fahrenheit, multiply the Celsius temperature by 9/5 (or 1.8) and then add 32. The formula is F = C times 9/5 plus 32. For example, 100 degrees Celsius equals (100 times 1.8) plus 32 = 212 degrees Fahrenheit. To convert the other direction, subtract 32 from the Fahrenheit temperature and multiply by 5/9. A useful shortcut for mental math: double the Celsius value and add 30 for a rough estimate. The two scales intersect at exactly -40, meaning -40 Celsius equals -40 Fahrenheit. Common reference points: 0 C = 32 F (water freezes), 37 C = 98.6 F (body temperature), 100 C = 212 F (water boils).
What is the Kelvin scale and why is it used in science?
The Kelvin scale is the SI unit of temperature and starts at absolute zero (0 K = -273.15 C), the theoretical lowest possible temperature where all molecular motion ceases. Unlike Celsius and Fahrenheit, Kelvin has no negative values, which makes it essential for thermodynamic calculations, gas laws, and radiation physics. The Kelvin scale uses the same degree size as Celsius (1 K = 1 C in magnitude), so converting is simple: add 273.15 to Celsius to get Kelvin. Water freezes at 273.15 K and boils at 373.15 K. The Kelvin scale is named after Lord Kelvin (William Thomson), who proposed it in 1848, and it is indispensable in fields like cryogenics, astrophysics, and materials science.
Why do the United States and most other countries use different temperature scales?
The Fahrenheit scale was developed by Daniel Gabriel Fahrenheit in 1724 and was widely adopted across the English-speaking world. Most countries later switched to Celsius (developed by Anders Celsius in 1742) as part of broader metric system adoption in the 19th and 20th centuries. The United States retained Fahrenheit largely due to the practical costs and cultural inertia of converting an entire nation's thermometers, weather reports, cooking recipes, and medical practices. Fahrenheit has some practical advantages for weather reporting: the 0-100 range roughly corresponds to the range of outdoor temperatures in temperate climates. Celsius is more scientific, with 0 and 100 corresponding to water freezing and boiling points.
What are the Delisle, Newton, Reaumur, and Romer scales?
These are historical temperature scales that predate or were contemporary with Celsius and Fahrenheit. The Delisle scale (1732) runs backwards, with 0 at the boiling point of water and 150 at the freezing point, and was used in Russia for about a century. The Newton scale was invented by Isaac Newton around 1700, using 0 for the freezing point and 33 for the boiling point of water. The Reaumur scale (1730) sets 0 at freezing and 80 at boiling, and was widely used in France, Germany, and Russia. The Romer scale (1701) by Ole Romer sets 7.5 at freezing and 60 at boiling. While no longer in common use, understanding them provides insight into the history of thermometry.
What is absolute zero and can it ever be reached?
Absolute zero is 0 Kelvin, -273.15 degrees Celsius, or -459.67 degrees Fahrenheit. It represents the theoretical temperature at which all atomic and molecular motion would cease completely. According to the third law of thermodynamics, absolute zero can never actually be reached, only approached asymptotically. Scientists have cooled atoms to within billionths of a degree above absolute zero using laser cooling and evaporative cooling techniques. At temperatures near absolute zero, matter exhibits exotic quantum behaviors such as Bose-Einstein condensation (where atoms merge into a single quantum state) and superconductivity (where electrical resistance drops to zero). These phenomena have practical applications in quantum computing and MRI technology.
How does temperature relate to heat and thermal energy?
Temperature measures the average kinetic energy of particles in a substance, while heat is the total thermal energy transferred between objects due to a temperature difference. Two objects can have the same temperature but vastly different amounts of thermal energy. For example, a cup of coffee at 80 degrees Celsius contains much less thermal energy than a swimming pool at 25 degrees Celsius, even though the coffee is hotter. Specific heat capacity determines how much energy is needed to raise one kilogram of a substance by one degree: water requires 4186 joules per kilogram per degree Celsius, while iron only requires 449. This distinction between temperature and heat is fundamental to thermodynamics and engineering.
What temperature reference points are most useful to remember?
Key temperature reference points span a wide range of practical and scientific significance. Absolute zero is -273.15 C (0 K), liquid nitrogen boils at -196 C, and dry ice (solid CO2) sublimes at -78.5 C. Water freezes at 0 C (32 F) and boils at 100 C (212 F) at standard pressure. Human body temperature is approximately 37 C (98.6 F), and comfortable room temperature is about 20-22 C (68-72 F). Common cooking temperatures include 180 C (350 F) for baking and 200 C (400 F) for roasting. In metals, lead melts at 327 C, aluminum at 660 C, and iron at 1538 C. The surface of the Sun is approximately 5500 C.
How does altitude affect boiling point temperature?
Water boiling point decreases with altitude because atmospheric pressure drops at higher elevations. At sea level (1 atm), water boils at 100 degrees Celsius. At 1500 meters (about 5000 feet, like Denver, Colorado), water boils at about 95 C. At 3000 meters (about 10,000 feet), water boils at approximately 90 C. At the summit of Mount Everest (8849 meters), water boils at only about 70 C. This lower boiling point means food takes longer to cook at high altitudes and requires recipe adjustments. Pressure cookers work on the opposite principle, increasing pressure above 1 atm to raise the boiling point and cook food faster. This relationship is described by the Clausius-Clapeyron equation.
What is the wind chill factor and how does it relate to actual temperature?
Wind chill is the perceived decrease in air temperature felt by the body due to air flow. Moving air accelerates heat loss from exposed skin, making the effective temperature feel lower than the actual thermometer reading. The wind chill index combines air temperature and wind speed into a single number representing the equivalent calm-air temperature. For example, an air temperature of -10 C with a 30 km/h wind produces a wind chill of approximately -20 C. Wind chill only applies to living organisms and exposed skin, not to inanimate objects or mechanical systems, which will cool to the actual air temperature regardless of wind. The current wind chill formula was adopted by the US and Canada in 2001 based on clinical trials measuring facial heat loss.
References
Reviewed for accuracy by Manoj Kumar, Mathematics Educator · Editorial policy
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