Temperature Conversion   | Celsius (°C) → Fahrenheit (°F)

Supported Units

Name	Description	Conversions
Celsius (°C)	The Celsius (°C) is a unit of temperature commonly used in most countries around the world. It is based on the freezing point of water at 0°C and the boiling point at 100°C, under standard atmospheric pressure. The Celsius scale is widely used in science, weather forecasting and daily life to measure temperature. Conversions: °C = (°F - 32) x 5/9 °C = K - 273.15 °C = °R x 5/9 - 273.15 °C = °Ré x 5/4 Features: Freezing Point of Water: 0°C (under standard atmospheric pressure) Boiling Point of Water: 100°C (under standard atmospheric pressure) Common Uses: Weather Forecasting Celsius is used globally (except in the U.S.) to report and predict air temperatures, helping people plan daily activities and prepare for extreme weather conditions. Cooking In kitchens, Celsius is used for setting oven temperatures, ensuring food safety (e.g., cooking meats to specific temperatures) and following recipes, particularly in baking and candy-making. Scientific Research Celsius is the standard for measuring temperature in scientific experiments, especially in fields like chemistry, biology and climate studies, ensuring consistent global communication of results.	°C = (°F - 32) x 5/9 °C = K - 273.15 °C = °R x 5/9 - 273.15 °C = °Ré x 5/4
Fahrenheit (°F)	The Fahrenheit (°F) scale is a temperature scale primarily used in the United States and its territories. It is based on the freezing and boiling points of water, but with different reference points than the Celsius scale. Conversions: °F = (°C x 9/5) + 32 °F = (K - 273.15) x 9/5 + 32 °F = °R - 459.67 °F = (°Ré x 9/4) + 32 Features: Freezing Point of Water: 32°F (under standard atmospheric pressure) Boiling Point of Water: 212°F (under standard atmospheric pressure) Common Uses: Weather Forecasting Fahrenheit is primarily used in the United States for reporting daily temperatures, helping people dress appropriately and plan activities. Home Heating and Cooling Thermostats in U.S. homes often display temperature in Fahrenheit to control indoor heating and air conditioning systems. Cooking Recipes, especially in the U.S., often provide oven temperatures in Fahrenheit for baking, roasting and grilling.	°F = (°C x 9/5) + 32 °F = (K - 273.15) x 9/5 + 32 °F = °R - 459.67 °F = (°Ré x 9/4) + 32
Kelvin (K)	The Kelvin (K) is the SI (International System of Units) unit for temperature. It is an absolute scale, meaning it starts at absolute zero, the theoretical point where all molecular motion ceases. Conversions: K = °C + 273.15 K = (°F - 32) x 5/9 + 273.15 K = °R x 5/9 K = (°Ré x 5/4) + 273.15 Features: Absolute Zero: 0 K, equivalent to -273.15°C No Negative Values: Kelvin temperatures are always positive because they are measured from absolute zero. Scale: Each increment of 1 K is equivalent to 1°C, so the size of the degree is the same as in Celsius. Common Uses: Scientific Research Kelvin is widely used in scientific fields like physics, chemistry and astronomy, where precise and absolute temperature measurements are needed. Temperature Measurement Kelvin is used in thermodynamics, particularly when dealing with gas laws and energy calculations.	K = °C + 273.15 K = (°F - 32) x 5/9 + 273.15 K = °R x 5/9 K = (°Ré x 5/4) + 273.15
Rankine (°R)	The Rankine (°R) is a temperature scale used primarily in thermodynamics, particularly in engineering and the U.S. for certain scientific applications. It is an absolute scale like Kelvin, but uses Fahrenheit degrees instead of Celsius degrees. Conversions: °R = (°C + 273.15) x 9/5 °R = °F + 459.67 °R = K x 9/5 °R = (°Ré x 9/4) + 491.67 Features: Absolute Zero: 0°R, equivalent to -459.67°F. Zero Point: 0°R represents absolute zero, the temperature at which molecular motion theoretically stops. Scale: The size of the degree is the same as Fahrenheit, meaning each increment of 1°R is equivalent to a 1°F change. Common Uses: Thermodynamic Systems In systems involving heat engines, particularly steam turbines and refrigeration cycles, the Rankine scale is often used to express temperatures in processes such as the Rankine cycle (the thermodynamic cycle used by steam engines). Energy Calculations It helps in calculating the work and efficiency of thermal systems, where temperature differences between heat sources and heat sinks are critical. Power Plant Engineering It is used to measure and calculate steam temperatures and pressures in power plants for efficient energy conversion. Engineering and Design Engineers use the Rankine scale when designing and analyzing systems that rely on heat exchange and energy conversion, such as HVAC systems, turbines, and jet engines.	°R = (°C + 273.15) x 9/5 °R = °F + 459.67 °R = K x 9/5 °R = (°Ré x 9/4) + 491.67
Réaumur (°Ré)	The Réaumur (°Ré) is a historical temperature scale, mostly used in Europe and some parts of the world until the 19th century. It is based on the freezing and boiling points of water, similar to Celsius, but with a different scale division. Conversions: °Ré = °C x 4/5 °Ré = (°F - 32) x 4/9 °Ré = (K - 273.15) x 4/5 °Ré = (°R - 491.67) x 4/9 Features: Freezing Point of Water: 0°Ré (at standard atmospheric pressure) Boiling Point of Water: 80°Ré (at standard atmospheric pressure) Scale: The scale is divided into 80 equal intervals between the freezing and boiling points of water, compared to 100 in Celsius. Common Uses: Historical Use: Once used in Europe for scientific and industrial purposes, but has largely been replaced by Celsius. Cooking and Industry It was used for certain industrial processes and in some regions for measuring temperature in cooking.	°Ré = °C x 4/5 °Ré = (°F - 32) x 4/9 °Ré = (K - 273.15) x 4/5 °Ré = (°R - 491.67) x 4/9

The Scales Explained

Celsius

Zero at the freezing point of water and 100 at its boiling point at standard pressure — a hundred degrees spanning the range in which most human activity happens. It is the everyday scale almost everywhere and the standard for science outside of thermodynamics.

Fahrenheit

Water freezes at 32 and boils at 212, giving 180 degrees between the two. Because its degrees are smaller than Celsius degrees, it offers finer resolution without decimals, which is part of why it persists for weather reporting in the United States.

Kelvin

The SI base unit. It starts at absolute zero, the point at which no further thermal energy can be extracted, and uses degrees the same size as Celsius degrees. Note that kelvin takes no degree sign: it is written 300 K, not 300 °K.

Rankine

An absolute scale like Kelvin, but with Fahrenheit-sized degrees. It exists so that engineers working in imperial units can do thermodynamic calculations without switching systems, and it still appears in some US engineering practice.

Réaumur

Zero at freezing and 80 at boiling. Largely historical now, it survives in a few specialist corners — some European cheese and syrup production still quotes it — and it turns up when reading older scientific literature.

Why Temperature Conversion Is Different

Most unit conversions are a single multiplication: a kilometer is always 1,000 meters, whatever the value. Temperature scales are not like that, because they disagree about both the size of a degree and where zero sits.

That means converting requires an offset as well as a factor. Going from Celsius to Fahrenheit is multiply by 9/5, then add 32 — omit the offset and every answer is wrong by 32 degrees. It also means ratios are meaningless on the relative scales: 20 °C is not "twice as hot" as 10 °C, because zero is an arbitrary point rather than an absence of heat.

On absolute scales, ratios do work. 300 K really does carry twice the thermal energy of 150 K, which is exactly why Kelvin and Rankine exist and why gas law calculations must use them.

Reference Points

• Absolute zero — −273.15 °C, −459.67 °F, 0 K, 0 °R.
• Water freezes — 0 °C, 32 °F, 273.15 K.
• Typical room temperature — 20 °C, 68 °F, 293.15 K.
• Human body temperature — about 37 °C, 98.6 °F.
• Water boils — 100 °C, 212 °F, 373.15 K, at standard pressure.
• The scales cross — −40 °C is exactly −40 °F, the one value where they agree.

Common Uses

• Cooking with foreign recipes — oven temperatures quoted in the other scale.
• Weather — making sense of a forecast while traveling.
• Science and laboratory work — converting to Kelvin for any calculation involving gas laws or thermodynamics.
• Engineering — Rankine for thermodynamic work carried out in imperial units.
• Medical readings — comparing body temperature between scales.
• Industrial specifications — equipment datasheets that state operating ranges in an unfamiliar unit.

Quick Mental Approximations

• Celsius to Fahrenheit — double it and add 30. For 20 °C that gives 70, against a true 68 °F: close enough for deciding on a jacket.
• Fahrenheit to Celsius — subtract 30 and halve. For 70 °F that gives 20, against a true 21.1 °C.
• Celsius to Kelvin — add 273. This one is nearly exact; the precise offset is 273.15.
• Use the exact conversion for anything that matters. The shortcuts drift further apart the further you get from ordinary temperatures.

Frequently Asked Questions

At what temperature do Celsius and Fahrenheit read the same?

At −40. It is the single point where the two scales coincide, which falls out of the fact that their degree sizes differ while their zero points are offset.

Why does Kelvin not use a degree symbol?

Because a kelvin is a unit in its own right rather than a degree on a relative scale. The SI convention is to write 300 K. Celsius and Fahrenheit keep the symbol because they measure position on a scale, not an absolute quantity.

What is absolute zero?

The lower limit of temperature: 0 K, or −273.15 °C. At that point a system holds the least energy quantum mechanics permits. It cannot be reached in practice, though laboratories have come within a billionth of a kelvin.

Which scale should I use for scientific work?

Kelvin for anything involving thermodynamics, gas laws, or ratios of temperature, since those require an absolute scale. Celsius is fine for reporting ordinary measurements and temperature differences — a change of one degree is the same in both.

Is a temperature difference converted the same way?

No, and this is a common error. For a difference you apply only the factor, not the offset: a rise of 10 °C is a rise of 18 °F, not 50 °F. The offset applies to points on the scale, not to intervals between them.