How do I convert Celsius to Fahrenheit?

Multiply by 9/5 (or 1.8) and add 32. For 25 °C, 25 × 1.8 = 45, and 45 + 32 = 77 °F.

How do I convert Fahrenheit to Celsius?

Subtract 32 and multiply by 5/9. For 68 °F, 68 − 32 = 36, and 36 × 5/9 = 20 °C.

At what temperature are Celsius and Fahrenheit the same?

-40. At -40 °C it is also -40 °F. You can check it: -40 × 9/5 + 32 = -72 + 32 = -40.

Can a temperature be below absolute zero?

No. Absolute zero is 0 K, which is -273.15 °C and -459.67 °F. The converter shows a message if you enter something colder.

Why does Kelvin not have a degree sign?

Because it is an absolute scale and since 1967 the unit is simply the kelvin. You write 300 K, not 300 °K.

Is anything I type stored or sent?

No. Typing sends nothing anywhere: the conversion runs in your browser. Your numbers are also kept in the page address so that Copy link works. That means a link you share, or a page you reload, requests that address, numbers included, from our server like any web address. Share a link only if you are happy to share the numbers.

Temperature Converter: Celsius, Fahrenheit and Kelvin

Conversion chart from degrees Celsius to degrees Fahrenheit
degree Celsius (°C)	degree Fahrenheit (°F)
-40	-40
-10	14
0	32
10	50
20	68
30	86
37	98.6
100	212

degree Celsius (°C)

degree Fahrenheit (°F)

-40

-10

98.6

100

212

At a glance

What it does

Converts between five temperature scales: degrees Celsius, degrees Fahrenheit, kelvin, degrees Rankine and degrees Réaumur.

Exactness

Uses exact fractions, so 37 °C is exactly 98.6 °F and -40 is the same on both scales. The answer is rounded once, at the end.

The rule in words

Under the answer you see the working, and for the common pairs the rule in plain words, such as multiply by 9/5 and add 32.

Absolute zero

Nothing can be colder than 0 K, -273.15 °C or -459.67 °F. The converter says so instead of giving a meaningless number.

Negative values

On a phone, a ± button next to the box switches the sign, because number keypads often have no minus key.

Privacy

Nothing is sent when you type. Your numbers are kept in the page address so Copy link works, so a shared link carries them.

Price

Free, no sign-up.

How to do it

Enter the temperature

Type or paste a number. Negative temperatures work: type -5 or use the ± button on a phone.

Choose the scales

Pick From and To. The menu has two groups: Everyday (degrees Celsius and degrees Fahrenheit) and Science and engineering (kelvin, degrees Rankine and degrees Réaumur). The swap button turns the conversion around.

Read the answer and the rule

The result updates as you type. Under it is the rule for this pair in words, and the working that goes through kelvin where needed.

Use the chart

Below the result is a chart of common temperatures, from -40 °C to 100 °C. The rows are written in the scale you are converting from, so from Fahrenheit they read -40, 14, 32, 50, 68, 86, 98.6 and 212, and from kelvin 233.15 to 373.15. The second column shows each row in the scale you are converting to.

Why temperature needs more than a multiplier

Most unit conversions are a single multiplication: feet to meters is times 0.3048. Temperature is different because the scales do not start at the same place. 0 °C is the freezing point of water and 0 °F is a much colder temperature, so converting needs an addition as well as a multiplication.

Between Celsius and Fahrenheit: °F = °C × 9/5 + 32 and °C = (°F − 32) × 5/9. Water freezes at 0 °C, which is 32 °F, and boils at 100 °C, which is 212 °F, at standard sea level pressure. One Celsius degree is 1.8 Fahrenheit degrees, so a 10 degree rise in Celsius is an 18 degree rise in Fahrenheit.

That last point is the most common mistake. This converter turns a temperature on one scale into the same temperature on another. It is not for converting a temperature change: if it got 10 °C warmer, it got 18 °F warmer, not 50 °F.

The five scales

Celsius (°C) is used for weather, cooking and body temperature in most of the world. It is defined from the kelvin: 0 °C is exactly 273.15 K.
Fahrenheit (°F) is used for everyday temperatures in the US and a few other places. Water freezes at 32 °F and boils at 212 °F, 180 degrees apart.
Kelvin (K) starts at absolute zero. It has the same size of step as Celsius, so K = °C + 273.15. It is written without a degree sign: since 1967 the unit is called the kelvin, not the degree Kelvin.
Rankine (°R) starts at absolute zero like kelvin but has the same size of step as Fahrenheit. It is used in some US engineering work. 0 °C is 491.67 °R.
Réaumur (°Ré) puts the freezing and boiling points of water at 0 and 80. It is historical, and turns up in older books and papers.

Landmark temperatures

Absolute zero: 0 K, -273.15 °C, -459.67 °F. Nothing can be colder.
Water freezes: 0 °C, 32 °F, 273.15 K.
Comfortable room: about 20 to 22 °C, which is 68 to 71.6 °F.
Normal body temperature: about 37 °C, 98.6 °F. Real body temperature varies between people and through the day.
Water boils: 100 °C, 212 °F, 373.15 K, at standard sea level pressure. It boils at a lower temperature on a mountain.
-40: the one temperature that is the same in Celsius and Fahrenheit.

For the two most common conversions on their own pages, see Celsius to Fahrenheit and Fahrenheit to Celsius.

Temperature converter