To convert Fahrenheit to Celsius, subtract 32 from the Fahrenheit temperature and then multiply the result by 5/9, which gives the formula C = (F − 32) × 5/9.
Fahrenheit (°F) is the everyday temperature scale in the United States, while Celsius (°C) is used across most of the world and in nearly all science. Converting between them is simple arithmetic once you know the two fixed points the scales agree on and the ratio between their degrees.
The exact formula
The conversion from Fahrenheit to Celsius is exact, not an approximation:
°C = (°F − 32) × 5/9
The 32 accounts for the offset between the two scales (water freezes at 32°F but 0°C), and the 5/9 factor accounts for the fact that a Celsius degree is larger than a Fahrenheit degree. There are 180 Fahrenheit degrees between the freezing and boiling points of water (32°F to 212°F) but only 100 Celsius degrees over the same range (0°C to 100°C). The ratio 100/180 reduces to 5/9.
Step by step
- Start with the Fahrenheit value you want to convert.
- Subtract 32 from it.
- Multiply the result by 5, then divide by 9 (or multiply by 0.5556).
- The answer is the temperature in degrees Celsius. Round to a sensible number of decimal places for your purpose.
For example, to convert 98.6°F (a common figure for normal body temperature): 98.6 − 32 = 66.6; 66.6 × 5 = 333; 333 ÷ 9 = 37. So 98.6°F equals exactly 37°C.
Common conversions at a glance
The table below lists reference points people convert most often. Values are rounded to one decimal place where they are not exact.
| Fahrenheit (°F) | Celsius (°C) | What it is |
|---|---|---|
| −40 | −40 | The one point where both scales read the same |
| 0 | −17.8 | Very cold winter day |
| 32 | 0 | Water freezes |
| 68 | 20 | Comfortable room temperature |
| 98.6 | 37 | Typical human body temperature |
| 212 | 100 | Water boils at sea level |
| 350 | 176.7 | A common baking oven setting |
| 450 | 232.2 | Hot oven for roasting |
A quick way to estimate in your head
When you do not need an exact figure, a good shortcut is to subtract 30 (instead of 32) and then halve the result. For a mild 70°F day this gives (70 − 30) ÷ 2 = 20°C, which is close to the true value of 21.1°C. The estimate drifts further from the real number at temperature extremes because you are using 1/2 instead of the true 5/9 (about 0.556), so reach for the full formula whenever accuracy matters, such as in cooking or medicine.
Why the two scales differ
Daniel Gabriel Fahrenheit introduced his scale in 1724, setting 0°F near the coldest temperature he could reliably reproduce with a brine mixture. Anders Celsius proposed his 100-degree scale in 1742, anchored to the freezing and boiling points of water. Because the two scales were built around different reference points and divide their range into a different number of degrees, no single multiplication converts one to the other — you always need both the subtraction and the ratio.
Handling negative temperatures
The formula works exactly the same below zero — you just keep track of the signs. Take 5°F on a cold day: 5 − 32 = −27; −27 × 5 = −135; −135 ÷ 9 = −15, so 5°F is −15°C. A common point of confusion is that 0°F is not 0°C; zero Fahrenheit is a bitterly cold −17.8°C. The scales only ever agree at −40 degrees, so any other value will read differently on each.
Rounding and precision
How many decimal places you keep depends on the job. For weather or casual conversation, rounding to the nearest whole degree is fine — saying 21°C for a 70°F afternoon is close enough. For cooking, aim for the nearest degree or half degree, since oven dials and thermometers rarely resolve finer than that. For science, engineering, or medicine, carry the full decimal from the formula and round only at the end, because rounding partway through a calculation can nudge the final figure off. Whatever you choose, do the subtraction and multiplication first and round last.
Converting the other direction
To go from Celsius back to Fahrenheit you reverse the operations: multiply by 9/5 and then add 32, so °F = (°C × 9/5) + 32. If you frequently switch between the two, it is worth learning both directions; our guide on how to convert Celsius to Fahrenheit walks through the reverse formula with the same worked examples. Note that Kelvin, the scale used in physics, shares Celsius’s degree size but starts at absolute zero, so you add 273.15 to a Celsius value to get Kelvin — a reminder that each scale answers a different need.
Where accurate conversion matters most
Cooking and baking are the everyday places small errors add up, since oven temperatures and candy or meat thermometers are often labeled in only one scale. Weather, travel, and home appliances are others: a thermostat set to 20°C is not the same as one set to 20°F. If you spend a lot of time converting kitchen measurements, you may also find our explainers on how many ounces are in a cup and how many tablespoons are in a cup useful, since recipes frequently mix unit systems for both temperature and volume.
Do calculators and phones do this automatically?
Yes. Most smartphone voice assistants, search engines, and weather apps convert instantly if you type a phrase like “100 F to C.” Spreadsheet users can apply the formula directly — in a program such as Excel or Google Sheets you would enter =(A1-32)*5/9 to convert a Fahrenheit value in cell A1. Learning the formula still helps you sanity-check whatever a tool reports and lets you convert when you are offline.
