Celsius to Fahrenheit Formula: How to Convert C to F (and F to C)

To convert Celsius to Fahrenheit, multiply by 1.8 (or 9/5) and add 32. To convert Fahrenheit to Celsius, subtract 32 and divide by 1.8 (or multiply by 5/9). That is the whole formula, in both directions.

If you just need an answer, the Celsius to Fahrenheit converter and the Fahrenheit to Celsius converter do it as you type. This guide works through both formulas with real examples, explains where the 1.8 and the 32 come from, gives you a chart of the temperatures people look up most, and shows which mental-math shortcuts are close enough to trust. We checked every number on this page by calculation, including how far off each shortcut gets.

9/5 and 1.8 are the same number, and so are 5/9 and ÷1.8. Use whichever is easier for the numbers in front of you. The one thing that matters is the order: going to Fahrenheit you multiply first and add 32 last; going to Celsius you subtract 32 first and divide last. Doing them the other way round is the most common mistake.

1. Take the temperature in Celsius.
2. Multiply it by 1.8 (or multiply by 9, then divide by 5).
3. Add 32. The result is the temperature in Fahrenheit.

Worked examples

• 25°C (a warm day): 25 × 1.8 = 45, and 45 + 32 = 77°F.
• 37°C (body temperature): 37 × 1.8 = 66.6, and 66.6 + 32 = 98.6°F.
• 180°C (a moderate oven): 180 × 1.8 = 324, and 324 + 32 = 356°F. Recipes round this to 350°F.
• −10°C (a cold winter day): −10 × 1.8 = −18, and −18 + 32 = 14°F. Keep the minus sign when you multiply; the 32 is still added afterwards.

1. Take the temperature in Fahrenheit.
2. Subtract 32.
3. Divide by 1.8 (or multiply by 5, then divide by 9). The result is the temperature in Celsius.

Worked examples

• 350°F (the most common oven setting): 350 − 32 = 318, and 318 ÷ 1.8 = 176.7°C. Recipes round this to 180°C.
• 98.6°F: 98.6 − 32 = 66.6, and 66.6 ÷ 1.8 = 37°C.
• 72°F (a typical thermostat setting): 72 − 32 = 40, and 40 ÷ 1.8 = 22.2°C.
• 0°F: 0 − 32 = −32, and −32 ÷ 1.8 = −17.8°C. Zero Fahrenheit is well below freezing.

The Fahrenheit to Celsius converter gives the same answers to six decimal places (350°F shows as 176.666667°C), and the swap button turns it round the other way.

Both scales are pinned to the same two points: the temperature at which water freezes and the temperature at which it boils (at normal sea-level air pressure).

• Water freezes at 0°C and 32°F.
• Water boils at 100°C and 212°F.

So the gap between freezing and boiling is 100 degrees on the Celsius scale and 180 degrees on the Fahrenheit scale. 180 ÷ 100 = 1.8: each Celsius degree is 1.8 Fahrenheit degrees wide. That is the multiplier. The 32 is there because the Fahrenheit scale starts counting 32 degrees below freezing, while Celsius starts at freezing. Multiply to fix the size of the degrees, add 32 to fix the starting point.

The two scales cross at exactly one temperature: −40°C = −40°F. It is the only number where you can skip the conversion. You can check it with the formula: −40 × 1.8 = −72, and −72 + 32 = −40.

The popular shortcut for Celsius to Fahrenheit is double it and add 30. It is quick and good enough for the weather, but its error grows the further you get from 10°C, where it happens to be exact. We calculated the error at common temperatures:

Between about 0°C and 25°C it stays within 3°F, which is fine for deciding on a jacket. Never use it for an oven or a fever: at 180°C it is 34°F out.

The exact version you can still do in your head

Double it, subtract a tenth of the result, then add 32. Doubling and taking away 10% is the same as multiplying by 1.8, so this is exact, not an approximation. For 37°C: double is 74, a tenth of 74 is 7.4, 74 − 7.4 = 66.6, plus 32 = 98.6°F.

Fahrenheit to Celsius in your head

The quick version is the reverse: subtract 30 and halve it. It is exact at 50°F and within about 3°C anywhere from 0°F to 100°F (at 100°F it gives 35°C against an exact 37.8°C). For an oven it is useless: 350°F comes out as 160°C instead of 176.7°C.

For a closer answer, subtract 32, halve it, then add a tenth of that. It lands within about 1% of the exact value: 212°F gives 99°C (exact: 100°C), and 350°F gives 174.9°C (exact: 176.7°C).

The temperatures people convert most often, calculated exactly and rounded to one decimal place:

For any value not listed, type it into the Celsius to Fahrenheit converter.

Recipes do not use exact conversions for ovens. They round to the nearest familiar setting, because oven dials are marked in steps of 25°F or 10°C and ovens are rarely accurate to a few degrees anyway. These are the standard pairs used in cookbooks, with the exact conversion alongside so you can see the rounding:

Fan ovens: many UK, European and Australian recipes list two temperatures, such as “180°C, 160°C fan”. The fan figure is usually about 20°C lower because circulating air cooks faster. If your oven is not a fan oven, use the higher number; if you are converting to Fahrenheit for a conventional US oven, convert the higher number too.

If the recipe also gives weights and volumes you need to convert, the cups to ml and ml to cups converters cover the kitchen side.

The formula is for converting a reading. If you are converting a difference between two temperatures, such as “it will be 10 degrees warmer tomorrow” or “the planet has warmed by 1.5°C”, you do not add 32. You only multiply by 1.8.

• A rise of 10°C is a rise of 18°F (not 50°F).
• A change of 1.5°C is a change of 2.7°F.
• A change of 2°C is a change of 3.6°F.
• Going the other way, divide by 1.8 and do not subtract 32: a 9°F drop is a 5°C drop.

The reason is that the 32 only shifts the starting point of the scale. A difference has no starting point, so the shift cancels out and only the size of the degree (1.8) is left. Online converters, including ours, assume you have typed a reading, so do this one by hand.

Excel, Google Sheets and LibreOffice

With the Celsius value in cell A2, either of these gives Fahrenheit:

=CONVERT(A2,"C","F")
=A2*9/5+32

And for Fahrenheit to Celsius:

=CONVERT(A2,"F","C")
=(A2-32)*5/9

CONVERT also accepts "K" for Kelvin. We ran these in LibreOffice Calc: 37 gave 98.6, 350 gave 176.666666666667, and 20°C to "K" gave 293.15. Wrap the formula in ROUND(..., 1) if you want one decimal place. Fill the formula down the column to convert a whole list at once.

Python

def c_to_f(c):
    return c * 9 / 5 + 32

def f_to_c(f):
    return (f - 32) * 5 / 9

print(c_to_f(37))            # 98.6
print(round(f_to_c(350), 1)) # 176.7

JavaScript

const cToF = (c) => c * 9 / 5 + 32;
const fToC = (f) => (f - 32) * 5 / 9;

cToF(-40); // -40
fToC(350); // 176.66666666666666

Both snippets were run as written and printed the values shown in the comments.

Celsius is the temperature scale used by almost every country and by science worldwide. Fahrenheit is used for everyday temperatures mainly in the United States, plus a handful of smaller countries and territories. If a weather forecast, thermostat or recipe comes from the US, assume Fahrenheit.

A Fahrenheit degree is smaller (1/1.8 of a Celsius degree), so Fahrenheit numbers change faster: a 10-degree swing in Fahrenheit is only about 5.6 degrees in Celsius. Both scales sit on the same physical temperatures, so there is no “more accurate” one. Scientists usually work in Kelvin, which uses Celsius-sized degrees but starts at absolute zero: 0 K is −273.15°C, or −459.67°F. To convert into Kelvin, use the Celsius to Kelvin or Fahrenheit to Kelvin converter.

Celsius to Fahrenheit: multiply by 1.8, then add 32. Fahrenheit to Celsius: subtract 32, then divide by 1.8. “Double and add 30” is fine for the weather and wrong for the oven. For a temperature change, skip the 32. And when you just want the number, the Celsius to Fahrenheit and Fahrenheit to Celsius converters do it as you type, free and in your browser.