What is the formula to convert Celsius to Fahrenheit?

The formula to convert Celsius (°C) to Fahrenheit (°F) is: F = (C × 9/5) + 32. For example, 100°C equals (100 × 1.8) + 32 = 180 + 32 = 212°F, which is the boiling point of water at sea level. To go the other way, from Fahrenheit to Celsius, use: C = (F - 32) × 5/9.

How do you convert Celsius to Kelvin?

To convert Celsius to Kelvin (K), simply add 273.15: K = C + 273.15. For example, 0°C (the freezing point of water) equals 273.15 K. Absolute zero, the coldest possible temperature, is 0 K, which equals -273.15°C. Kelvin uses the same scale intervals as Celsius but starts at absolute zero, so no degree symbol is used with Kelvin.

What is the difference between Celsius and Fahrenheit?

Celsius and Fahrenheit are both temperature scales, but they use different reference points and intervals. On the Celsius scale, 0°C is the freezing point of water and 100°C is the boiling point at sea level. On the Fahrenheit scale, those same points are 32°F and 212°F. The scales cross at -40° (that is, -40°C equals -40°F). Celsius is used in most of the world including New Zealand. Fahrenheit is used mainly in the United States.

Celsius Converter

This calculator converts a temperature you enter in degrees Celsius into Fahrenheit, Kelvin and Rankine, updating instantly as you type so you can move between scales without doing the maths by hand. Type any Celsius value into the input box, or use the quick-select dropdown to jump straight to a common reference point such as absolute zero, liquid nitrogen's boiling point, dry ice sublimation, the -40 degree crossover where Celsius and Fahrenheit agree, freezing and boiling water, room and body temperature, or the melting point of gold. The calculator returns your Fahrenheit, Kelvin and Rankine equivalents, rounded to two decimal places, alongside a step-by-step working panel that shows exactly how each figure is derived from the formulas F = (C x 9/5) + 32, K = C + 273.15 and R = (C + 273.15) x 9/5. Kelvin is exact by SI definition, since it uses the same size of degree as Celsius but starts at absolute zero, while Fahrenheit and Rankine use a smaller degree interval and different zero points. Below the converter you will find a quick-reference table listing these same scales for common temperatures, handy for checking oven settings, weather forecasts, or scientific readings without re-entering numbers each time. Celsius is the standard scale used across New Zealand, so this tool is handy whenever you need to compare with a Fahrenheit or Kelvin reading.

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Standard conversions Based on exact SI definitions. 0 K = -273.15°C (exact).

Temperature in Celsius

Celsius temperature (°C)

°C

Quick select a reference temperature

Conversion Formulas

The exact formulas used by this converter:

°F = (°C × 9/5) + 32

K = °C + 273.15

°R = (°C + 273.15) × 9/5

The Kelvin conversion is exact by SI definition. Fahrenheit and Rankine results are rounded to 2 decimal places.

Conversion Results

Fahrenheit
212.00
°F

Kelvin

373.15

Rankine

671.67

°R

Step-by-Step Working

Input temperature100°C

Celsius to Fahrenheit: (°C × 9/5) + 32(100 × 1.8) + 32 = 212.00°F

Celsius to Kelvin: °C + 273.15100 + 273.15 = 373.15 K

Celsius to Rankine: (°C + 273.15) × 9/5373.15 × 1.8 = 671.67°R

Common Temperature Reference Table

Temperature	Celsius (°C)	Fahrenheit (°F)	Kelvin (K)	Rankine (°R)
Absolute zero	-273.15	-459.67	0	0
Freezing point of water	0	32.00	273.15	491.67
Room temperature	20	68.00	293.15	527.67
Body temperature	37	98.60	310.15	558.27
Boiling point of water	100	212.00	373.15	671.67
-40°C = -40°F crossover	-40	-40.00	233.15	419.67

How the Celsius Scale Works

The Celsius scale (formerly called Centigrade) was defined so that 0°C is the freezing point of pure water at standard atmospheric pressure and 100°C is the boiling point of pure water at the same pressure. This made it intuitive and practical for everyday use. Today, the Celsius scale is formally defined in terms of Kelvin: 0°C = 273.15 K exactly.

New Zealand, like most countries outside the United States, uses Celsius for weather forecasts, cooking, body temperature, and industry. You will see Celsius on NZ thermometers, ovens (which use fan-bake settings in Celsius), and medical readings.

Converting Celsius to Fahrenheit

The conversion formula is: F = (C × 9/5) + 32, which can also be written as F = (C × 1.8) + 32. The 9/5 factor comes from the fact that there are 180 Fahrenheit degrees between the freezing and boiling points of water, and only 100 Celsius degrees, so each Celsius degree is 1.8 times as large as a Fahrenheit degree. The +32 offset adjusts for the different zero point.

A useful mental shortcut: double the Celsius temperature and add 30. This gives a quick approximation (for example, 20°C: 20 × 2 + 30 = 70, actual is 68°F). For cold temperatures, the approximation becomes less accurate.

Converting Celsius to Kelvin

Kelvin is the SI base unit for thermodynamic temperature. To convert Celsius to Kelvin, add 273.15. The Kelvin scale has no negative values: its zero point (absolute zero, 0 K) is the coldest theoretically possible temperature, equal to -273.15°C. Unlike Celsius and Fahrenheit, Kelvin does not use a degree symbol. You write 373.15 K, not 373.15°K. Kelvin is used extensively in physics, chemistry, and engineering.

Celsius to Rankine

Rankine is an absolute temperature scale based on Fahrenheit. It is used in some engineering applications in the United States. To convert, first convert Celsius to Kelvin (add 273.15), then multiply by 9/5. Equivalently: R = (C + 273.15) × 1.8. At absolute zero, Rankine is 0°R (same absolute starting point as Kelvin, but using Fahrenheit-sized degrees).

Worked Example: 100°C

Using the default value of 100°C (boiling point of water at sea level):

Fahrenheit: (100 × 9/5) + 32 = 180 + 32 = 212.00°F
Kelvin: 100 + 273.15 = 373.15 K
Rankine: 373.15 × 9/5 = 671.67°R

These match the results shown by the calculator above with the default input of 100°C.

Related Calculators

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Temperature Conversion: broader multi-scale temperature converter.

Method: Celsius to Fahrenheit: F = (C × 9/5) + 32. Celsius to Kelvin: K = C + 273.15 (exact SI definition, BIPM). Celsius to Rankine: R = (C + 273.15) × 9/5. Reference: Bureau International des Poids et Mesures (BIPM), The International System of Units (SI), 9th edition, 2019.

This converter uses exact SI-defined formulas. Results are rounded to two decimal places for display. Boiling and freezing points quoted are at standard atmospheric pressure (101.325 kPa). Actual boiling points vary with altitude and pressure.