Temperature Conversion Calculator

This calculator converts a temperature between the three scales in common use: Celsius, Fahrenheit and Kelvin. Knowing how to move between scales matters whenever you are reading an overseas recipe, checking an oven temperature, following a US weather report, or working with scientific data that uses Kelvin. You choose the scale you are converting from, Celsius, Fahrenheit or Kelvin, then type in a temperature value, or simply pick a common reference point such as body temperature, room temperature, freezing point or absolute zero from the preset list. As soon as you enter a number the calculator instantly returns the equivalent reading in all three scales at once, highlighting the scale you started from, so you can see, for example, that 100 degrees Celsius equals 212 degrees Fahrenheit and 373.15 Kelvin. Below the results you will find the exact conversion formulas used for each pairing, plus a reference table of everyday temperatures, from absolute zero and the freezing point of water through to body temperature, oven heat and boiling point, shown side by side in all three scales. The calculator uses the exact BIPM-defined constants, so figures are accurate to the decimal places you enter rather than rounded approximations, and it flags any entry below absolute zero (-273.15 degrees Celsius), since temperatures cannot physically go lower than that.

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Standard formulas BIPM (International Bureau of Weights and Measures) definitions. Exact conversion constants.

Enter a Temperature

Scale to convert from

Temperature value

°C

Please enter a valid number.

Common Presets

Quick reference temperature

Select a preset to populate the input on the left automatically.

Converted Temperatures

Celsius

100.00

degrees Celsius (°C)

Fahrenheit
212.00
degrees Fahrenheit (°F)

Kelvin

373.15

Kelvin (K)

Celsius to Fahrenheit

F = (C × 9/5) + 32

Fahrenheit to Celsius

C = (F − 32) × 5/9

Celsius to Kelvin

K = C + 273.15

Common Temperature Reference Points

Reference point	Celsius (°C)	Fahrenheit (°F)	Kelvin (K)
Absolute zero	-273.15	-459.67	0
Freezing point of water	0	32	273.15
Cold winter day	-10	14	263.15
Comfortable room temperature	20	68	293.15
Normal human body temperature	37	98.6	310.15
Celsius equals Fahrenheit	-40	-40	233.15
Boiling point of water (at sea level)	100	212	373.15
Oven (moderate heat)	180	356	453.15

How Temperature Conversion Works

Temperature is a measure of the average kinetic energy of particles in a substance. Three scales are in common use: Celsius, Fahrenheit, and Kelvin. Each has a different zero point and a different scale interval, so converting between them requires a two-step process rather than a simple multiplication.

The Three Temperature Scales

Celsius (°C) is the scale used in New Zealand, Australia, and most of the world for everyday temperature measurement. It was designed so that 0 °C is the freezing point of water and 100 °C is the boiling point of water at sea level. The degree Celsius is the same size as the Kelvin.

Fahrenheit (°F) is used in the United States and a small number of other countries. On this scale, water freezes at 32 °F and boils at 212 °F. The gap between freezing and boiling is 180 Fahrenheit degrees, compared to 100 Celsius degrees, so 1 °C equals 1.8 °F.

Kelvin (K) is the SI unit of temperature used in science and engineering. It shares the same scale interval as Celsius (one Kelvin equals one degree Celsius), but its zero point is absolute zero (-273.15 °C), the lowest temperature theoretically possible. Kelvin values are never negative in normal usage. Note that Kelvin is written without a degree symbol.

Conversion Formulas

To convert	Formula	Example
Celsius to Fahrenheit	F = (C × 9/5) + 32	100 °C = 212 °F
Fahrenheit to Celsius	C = (F − 32) × 5/9	98.6 °F = 37 °C
Celsius to Kelvin	K = C + 273.15	100 °C = 373.15 K
Kelvin to Celsius	C = K − 273.15	373.15 K = 100 °C
Fahrenheit to Kelvin	K = (F − 32) × 5/9 + 273.15	212 °F = 373.15 K
Kelvin to Fahrenheit	F = (K − 273.15) × 9/5 + 32	373.15 K = 212 °F

Worked Example (Default Values)

Starting with 100 °C (the boiling point of water at sea level):

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

These are the values shown in the results card above when the calculator loads.

Quick Mental Shortcuts

For everyday use, a quick approximation for Celsius to Fahrenheit is to double the Celsius value and add 30. This is not exact but is handy for mental arithmetic. For example, 20 °C gives 40 + 30 = 70 °F (exact is 68 °F). For Fahrenheit to Celsius, subtract 30 and halve the result: 70 °F gives (70 - 30) / 2 = 20 °C (exact is 21.1 °C).

The unique crossover point where Celsius and Fahrenheit readings are equal is -40 degrees. At that temperature, -40 °C = -40 °F.

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Method: Formulas as defined by the International Bureau of Weights and Measures (BIPM). The Celsius-Kelvin offset (273.15) is exact by definition of the SI temperature scale. The Celsius-Fahrenheit conversion constants (9/5 and 32) are exact. Boiling and freezing points of water are at standard atmospheric pressure (101.325 kPa).

This calculator converts between the three most widely used temperature scales using exact formulas. Boiling and freezing points quoted are for pure water at sea-level atmospheric pressure and will vary at altitude or with dissolved substances.

Frequently asked questions

How do you convert Celsius to Fahrenheit?

To convert Celsius to Fahrenheit, multiply by 9/5 and then add 32. The formula is: F = (C x 9/5) + 32. For example, 100 degrees Celsius equals (100 x 1.8) + 32 = 212 degrees Fahrenheit. A quick mental shortcut is to double the Celsius value and add 30, which gives a rough but useful approximation for everyday temperatures.

How do you convert Fahrenheit to Celsius?

To convert Fahrenheit to Celsius, subtract 32 and then multiply by 5/9. The formula is: C = (F - 32) x 5/9. For example, 98.6 degrees Fahrenheit equals (98.6 - 32) x 5/9 = 37 degrees Celsius. A quick mental check: 32 F is freezing (0 C), 68 F is a warm room (20 C), and 212 F is boiling (100 C).

What is absolute zero in Celsius and Fahrenheit?

Absolute zero is the lowest theoretically possible temperature, where particles have minimum thermal energy. It is defined as 0 Kelvin (K), which equals -273.15 degrees Celsius or -459.67 degrees Fahrenheit. At absolute zero, all classical molecular motion stops. This temperature has never been fully achieved in practice, though scientists have reached within billionths of a degree of it in laboratory conditions.

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