What is the formula for Celsius to Fahrenheit?

Multiply by 9/5 and add 32. So 20u00b0C becomes 20 u00d7 1.8 = 36, plus 32 = 68u00b0F. Going the other way, subtract 32 first and then multiply by 5/9.

Is there a temperature where Celsius and Fahrenheit are the same?

Yes, at minus 40. Both scales read u221240 at that point, which makes it a useful sanity check: if you convert u221240u00b0C and do not get u221240u00b0F, the formula has been applied the wrong way round.

Temperature Converter

Q: Is there a quick way to estimate Celsius to Fahrenheit in my head?

Double the Celsius value and add 30. For 20u00b0C that gives 70, against a true value of 68. The estimate drifts further apart at the extremes, but between about 5u00b0C and 30u00b0C it stays within a few degrees, which is close enough for deciding what to wear.

Convert between Celsius, Fahrenheit and Kelvin, with the formula shown for each conversion.

Temperature conversion formulas

Temperature conversions use fixed formulas. Unlike unit conversions based on multiplication alone, Fahrenheit and Celsius have different zero points, so conversion requires both multiplication and addition.

Celsius to Fahrenheit

°F = (°C × 9/5) + 32

Multiply by 9, divide by 5, then add 32. For example: 100 °C × 9 ÷ 5 + 32 = 212 °F.

Fahrenheit to Celsius

°C = (°F − 32) × 5/9

Subtract 32 first, then multiply by 5 and divide by 9. For example: (98.6 °F − 32) × 5 ÷ 9 = 37.0 °C.

Celsius to Kelvin

K = °C + 273.15

Kelvin is the SI unit for thermodynamic temperature and starts at absolute zero (−273.15 °C). It is used in physics, chemistry, and engineering where negative temperatures are not meaningful.

Fahrenheit to Kelvin

K = (°F + 459.67) × 5/9

Reference points

Celsius	Fahrenheit	What it is
−40°C	−40°F	Where the two scales meet
0°C	32°F	Water freezes
10°C	50°F	Cool day
20°C	68°F	Room temperature
37°C	98.6°F	Human body temperature
100°C	212°F	Water boils at sea level
180°C	356°F	A moderate oven
200°C	392°F	Moderate oven heat for roasting

Where each scale is used

Fahrenheit is standard in the United States and a few territories. Celsius is used almost everywhere else, including in scientific and medical contexts inside the US. Kelvin appears in physics and chemistry, where a scale with no negative numbers makes the maths simpler.

Cooking is the place this causes the most trouble. American recipes give oven temperatures in Fahrenheit and most of the world sets ovens in Celsius, so 350°F becomes 177°C. Ovens are usually set in round numbers, so 180°C is the practical equivalent.

Why two scales exist

Daniel Gabriel Fahrenheit proposed his scale in 1724, using the freezing point of a salt-water mixture as 0° and human body temperature as 96° (later refined to 98.6°). Anders Celsius proposed his scale in 1742, using 0° for boiling and 100° for freezing — which was later reversed to the convention we use today. The Fahrenheit scale is still used for everyday weather and cooking in the United States and a few other countries. The Celsius scale is used in science worldwide and in everyday life in most countries.

Cooking temperature guide

Low oven: 120–150 °C (250–300 °F) — slow cooking, meringues, dried herbs
Moderate oven: 160–180 °C (325–350 °F) — cakes, biscuits, roasted vegetables
Hot oven: 190–220 °C (375–425 °F) — bread, pastry, pizza bases
Very hot oven: 230–250 °C (450–480 °F) — pizzas, searing meats

Body temperature guide

Hypothermia risk: below 35 °C / 95 °F
Normal: 36.1–37.2 °C / 97–99 °F
Low-grade fever: 37.3–38.3 °C / 99.1–100.9 °F
Fever: 38.4–40 °C / 101.1–104 °F
Seek medical attention: above 40 °C / 104 °F

Common questions

Multiply by 9/5 and add 32. So 20°C becomes 20 × 1.8 = 36, plus 32 = 68°F. Going the other way, subtract 32 first and then multiply by 5/9.

Because the two scales do not share a zero point. Celsius puts zero at the freezing point of water and Fahrenheit puts it 32 degrees lower. Any conversion between them needs both a multiplication and an offset, which is why doubling a Celsius value does not double the Fahrenheit one.

Yes, at minus 40. Both scales read −40 at that point, which makes it a useful sanity check: if you convert −40°C and do not get −40°F, the formula has been applied the wrong way round.

Scientific work, because it starts at absolute zero and has no negative values. A Kelvin degree is the same size as a Celsius degree, so converting between them is just adding or subtracting 273.15. Room temperature of 20°C is 293.15 K.

Double the Celsius value and add 30. For 20°C that gives 70, against a true value of 68. The estimate drifts further apart at the extremes, but between about 5°C and 30°C it stays within a few degrees, which is close enough for deciding what to wear.

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