Fahrenheit to Celsius Converter

Fahrenheit to Celsius formula

Subtract 32 from the Fahrenheit temperature, then multiply by 5/9. Example: 68 °F − 32 = 36, and 36 × 5/9 = 20 °C. This is the exact inverse of the Celsius to Fahrenheit formula.

1. Subtract 32 from the Fahrenheit temperature to remove the offset between the two zero points.
2. Multiply by 5/9 (about 0.5556), because a Fahrenheit degree is only 5/9 the size of a Celsius degree.
3. The result is the temperature in degrees Celsius.

For a quick mental estimate, subtract 30 and halve the result: 80 °F → (80 − 30) ÷ 2 = 25 °C (exact: 26.7 °C).

Common Fahrenheit to Celsius conversions

Why the formula is “subtract 32, then multiply by 5/9”

Fahrenheit and Celsius differ in two ways. First, their zero points are in different places: water freezes at 32 °F but at 0 °C. Second, their degrees are different sizes: 180 Fahrenheit degrees cover the same range as 100 Celsius degrees, so one Fahrenheit degree is 100/180 = 5/9 of a Celsius degree.

The order of the steps follows from that. You first remove the 32-degree offset so that both scales start from the freezing point of water, and only then shrink the number by 5/9. Doing it the other way round — multiplying first and subtracting 32 afterwards — gives the wrong answer for every temperature except −40.

If decimals are easier than fractions, multiply by 0.5556 instead of 5/9; for exact work, divide by 1.8, which is the same thing as multiplying by 5/9.

Worked examples

Here is the formula applied step by step to some temperatures people convert most often — freezing, a comfortable room, body temperature, a very cold day and a hot oven.

Notice that 0 °F is well below freezing: -17.78 °C. The Fahrenheit zero was never meant to mark the freezing point of water, which is why negative Fahrenheit readings only occur in genuinely severe cold.

Fahrenheit to Celsius for weather

If you are travelling to the United States or reading an American forecast, these values give a quick feel for what the numbers mean. As a rough guide, every 9 °F step is a 5 °C step.

For the effect of wind or humidity on how the temperature feels, see the wind chill and heat index calculators.

Converting American oven temperatures

American recipes give oven temperatures in Fahrenheit, usually in steps of 25 °F. Ovens are not accurate to the degree, so the Celsius figure is normally rounded to the nearest 10 °C. The table shows both the exact conversion and the setting you would actually use.

If your oven has a fan (convection) setting, lower the Celsius figure by about 20 °C, or follow the manufacturer's guidance. For air fryers, see the oven to air fryer converter.

Food safety temperatures

Food-safety guidance in the United States is published in Fahrenheit. These are the key figures with their Celsius equivalents; use a food thermometer in the thickest part of the food, away from bone.

For a fuller list of doneness temperatures by type of meat, use the meat temperature calculator. Fridge and freezer settings are covered in the fridge and freezer temperature guide.

Body temperature from Fahrenheit to Celsius

98.6 °F is exactly 37 °C, the traditional figure for normal body temperature, although healthy readings range roughly from 97 °F to 99 °F (36.1–37.2 °C). A reading of 100.4 °F (38 °C) or higher is commonly treated as a fever, and 103 °F is 39.4 °C.

This is general information, not medical advice. If you are concerned about a temperature reading, contact a healthcare professional. See the fever temperature chart for a fuller table.

Quick mental estimate: subtract 30, then halve

When you just need a rough idea, subtract 30 from the Fahrenheit temperature and divide by 2. It is surprisingly close for everyday weather but drifts badly at high temperatures, so do not use it for cooking or medicine.

Converting a change in Fahrenheit

A temperature change is converted differently from a temperature reading. If it gets 18 °F warmer, that is a rise of 10 °C, not −7.8 °C. For a difference, skip the subtraction and just multiply by 5/9: a 9 °F change is 5 °C, and a 1 °F change is about 0.56 °C.

Fahrenheit around the house

Even outside the kitchen, many everyday settings in American homes are given in Fahrenheit. These are the ones people most often need in Celsius:

Thermostat advice is often expressed as “set it back 7–10 °F for eight hours a day”. Because that is a change rather than a reading, it is 3.9–5.6 °C. The thermostat savings calculator estimates what a setback is worth.

Why Fahrenheit is still used

Fahrenheit survives mainly in the United States, where it is built into everyday habits, appliances, building codes and decades of recipes and weather records. Supporters point out that its smaller degree gives whole-number precision for weather without decimals, and that 0–100 °F roughly spans the range of outdoor temperatures in much of the country, from a very cold winter day to a very hot summer one.

Science, medicine and international trade use Celsius and kelvin, so many Americans meet both scales: Fahrenheit on the weather app and Celsius in a laboratory, a hospital chart or a product made for export. Being able to move between them quickly — exactly with the formula, or roughly with the “subtract 30 and halve” trick — is a genuinely practical skill.

Common mistakes to avoid

• Multiplying before subtracting. (68 × 5/9) − 32 = 5.8 is wrong; (68 − 32) × 5/9 = 20 °C is right.
• Using 9/5 instead of 5/9. 9/5 is for Celsius to Fahrenheit; going from Fahrenheit you always end with a smaller number of degrees.
• Losing the minus sign. Anything below 32 °F becomes negative in Celsius: 14 °F is −10 °C.
• Adding or subtracting 32 for a change. Differences only need the 5/9 factor.

Frequently asked questions

Related pages

• 20 Celsius to Fahrenheit
• 18 Celsius to Fahrenheit
• 22 Celsius to Fahrenheit
• 25 Celsius to Fahrenheit
• 10 Celsius to Fahrenheit
• How to Convert Celsius to Fahrenheit
• Celsius to Fahrenheit Formula
• Celsius to Fahrenheit Chart