How do I convert Celsius to Fahrenheit?

Multiply by 9/5 and add 32. For a quick mental estimate, double the Celsius figure and add 30, which is accurate to within a couple of degrees in everyday ranges.

At what temperature are Celsius and Fahrenheit equal?

Minus 40. It is the single point where the two scales give the same number.

Why does Fahrenheit start freezing at 32?

Fahrenheit calibrated his scale against a brine freezing point and human body temperature rather than pure water, which left water freezing at 32 degrees.

What is absolute zero?

Zero Kelvin, equal to minus 273.15 Celsius. It is the theoretical point at which molecular motion ceases, and nothing can be colder.

Temperature Converter - Celsius, Fahrenheit & Kelvin

Temperature Converter

Convert between the three temperature scales for cooking, travel, weather or science, with the formulas shown so you can check the result by hand.

Formula

°F = (°C × 9/5) + 32 · °C = (°F − 32) × 5/9

K = °C + 273.15

20°C: (20 × 9/5) + 32 = 68°F

The Formulas

Celsius to Fahrenheit: (°C × 9/5) + 32
Fahrenheit to Celsius: (°F − 32) × 5/9
Celsius to Kelvin: °C + 273.15

The 32 exists because the Fahrenheit scale puts freezing at 32 rather than 0, and the 9/5 because a Fahrenheit degree is a smaller interval than a Celsius one.

Reference Points Worth Knowing

Water freezes: 0°C = 32°F = 273.15 K
Room temperature: 20°C = 68°F
Body temperature: 37°C = 98.6°F
Water boils: 100°C = 212°F
The scales meet: −40°C = −40°F

For rough mental conversion, double the Celsius figure and add 30. At 20°C that gives 70 against a true 68 — close enough to judge what to wear.

Kelvin and Absolute Zero

Kelvin starts at absolute zero, the point where molecular motion stops, so there are no negative Kelvin values. A Kelvin and a Celsius degree are the same size, which is why converting between them is simple addition. Note that Kelvin takes no degree symbol: 300 K, not 300°K.

Quick Reference

Reference points across the three scales.
Celsius	Fahrenheit	Kelvin	Reference
−273.15	−459.67	0	Absolute zero
0	32	273.15	Water freezes
20	68	293.15	Room temperature
37	98.6	310.15	Body temperature
100	212	373.15	Water boils

Frequently Asked Questions

How do I convert Celsius to Fahrenheit?: Multiply by 9/5 and add 32. For a quick mental estimate, double the Celsius figure and add 30, which is accurate to within a couple of degrees in everyday ranges.
At what temperature are Celsius and Fahrenheit equal?: Minus 40. It is the single point where the two scales give the same number.
Why does Fahrenheit start freezing at 32?: Fahrenheit calibrated his scale against a brine freezing point and human body temperature rather than pure water, which left water freezing at 32 degrees.
What is absolute zero?: Zero Kelvin, equal to minus 273.15 Celsius. It is the theoretical point at which molecular motion ceases, and nothing can be colder.

Read the full guide

Celsius to Fahrenheit: The Ultimate Temperature Conversion Guide