🌡️ Fahrenheit to Celsius Converter (F to C)

What is the Fahrenheit to Celsius Converter?

The Fahrenheit scale was proposed by Daniel Gabriel Fahrenheit in 1724, fixing the freezing point of water at 32 degrees and body temperature near 96 (later refined to 98.6). The Celsius scale, introduced by Anders Celsius in 1742, is simpler: water freezes at 0 and boils at 100 at sea level. Because the two scales share the same physical points but slice them into a different number of degrees, converting between them takes both a shift and a scaling step.

Between freezing and boiling there are 180 Fahrenheit degrees (212 - 32) but only 100 Celsius degrees. That ratio, 100/180, reduces to 5/9, which is the exact factor in the formula. To go from Fahrenheit to Celsius you first subtract 32 to line the freezing points up at zero, then multiply by 5/9 to rescale the size of each degree. So C = (F - 32) x 5/9. If you prefer whole-number arithmetic, the identical formula is C = (F - 32) x 5 / 9: subtract 32, multiply by 5, then divide by 9.

The reverse direction simply undoes those two steps in the opposite order: multiply the Celsius value by 9/5, then add 32 back on. That gives F = C x 9/5 + 32. The two formulas are exact inverses, so converting a number one way and then back returns the original value. A useful sanity check is minus 40, the single point where both scales read the same: -40 F equals -40 C. This is not a coincidence but a direct consequence of the linear relationship between the scales.

The United States is one of only a handful of places, alongside Belize, the Bahamas and the Cayman Islands, that still uses Fahrenheit for everyday temperatures, according to HowStuffWorks. The rest of the world runs on Celsius, which is why travellers, cooks following American recipes and students working across textbooks all need a reliable conversion. Fahrenheit does have one practical merit: it packs more whole-number degrees into the range of common outdoor temperatures, so 70 F and 71 F are a finer step apart than 21 C and 22 C.

Precision matters most for scientific, medical and cooking use. A tenth of a degree can be the difference between a normal and a feverish body temperature, so keep at least one decimal place there. For weather and everyday conversions, rounding to the nearest whole degree is fine, and for ovens most charts round to the nearest 5 C because domestic ovens are not accurate to a single degree. The common trap is rounding the 5/9 factor to 0.55 or 0.56 too early, which drifts noticeably at high temperatures; this tool keeps the exact fraction and only rounds the final answer.

A quick mental shortcut for weather is to subtract 30 and halve the result, so 70 F is roughly (70 - 30) / 2 = 20 C. It is close but not exact because it uses 0.5 instead of the true 0.5555 factor, and the error grows the further you move from typical air temperatures. For anything that must be right, such as medicine, lab work or precise baking, use the exact formula or this calculator rather than the shortcut.

When to use it

• Reading a US weather forecast in Fahrenheit and converting it to Celsius before a trip abroad.
• Checking whether a body temperature like 100.4 F counts as a fever in Celsius (38 C).
• Converting an American recipe oven setting, such as 350 F, to the 177 C used on European ovens, or to a UK gas mark.
• Doing science, chemistry or engineering homework where measurements are given in Fahrenheit but answers are needed in Celsius.
• Setting a thermostat, fridge or freezer correctly when the manual or appliance uses the other scale.
• Comparing climate or travel data between US sources (Fahrenheit) and international sources (Celsius).

How to use the Fahrenheit to Celsius Converter

1. Type a temperature into the Fahrenheit box (it starts at 98.6 F as an example).
2. Read the Celsius result, which updates instantly as you type.
3. To convert the other way, type a value into the Celsius box instead and read the Fahrenheit result.
4. Use a preset button for common points like freezing, boiling or oven temperature, or press Clear to start over.

Formula & method

Worked examples

Fahrenheit to Celsius conversion chart for common temperatures

Oven temperature conversion: Fahrenheit, Celsius and UK gas mark

Body temperature reference in Fahrenheit and Celsius

Common mistakes to avoid

• Multiplying before subtracting. The order matters: you must subtract 32 first, then multiply by 5/9. Multiplying 98.6 by 5/9 before subtracting gives the wrong answer. Follow (F - 32) inside the brackets first.
• Rounding the 5/9 factor too early. Using 0.55 or even 0.56 instead of the exact 5/9 (0.5555...) introduces error that grows at higher temperatures. Keep the exact fraction and only round the final result.
• Confusing the two directions. Fahrenheit to Celsius uses 5/9 and subtracts 32; Celsius to Fahrenheit uses 9/5 and adds 32. Mixing the factors or the plus and minus signs flips the conversion and produces a value that is far off.
• Forgetting that negatives are valid. Temperatures below zero are real: -10 F is about -23.3 C. Do not drop the minus sign or assume an error. The conversion works exactly the same way for negative numbers.
• Trusting the halve-and-subtract shortcut for precise work. The "subtract 30 and halve" trick is fine for glancing at the weather but uses 0.5 instead of 0.5555. For medicine, lab work or baking, use the exact formula or this calculator.
• Over-rounding oven temperatures the wrong way. 350 F is 176.67 C, which most charts round to 175 C, and 400 F is 204.44 C, usually shown as 200 C. Rounding to a random number instead of the standard oven step can leave you 10 degrees off.

Glossary

Fahrenheit

A temperature scale where water freezes at 32 degrees and boils at 212 degrees at sea level, used mainly in the United States.

Celsius

A temperature scale where water freezes at 0 degrees and boils at 100 degrees at sea level, used in most of the world. Also called centigrade.

Conversion factor

The number that rescales one unit into another. For Fahrenheit to Celsius it is 5/9, and for Celsius to Fahrenheit it is 9/5.

Freezing point

The temperature at which water turns to ice: 32 F or 0 C, used as one anchor for the conversion.

Boiling point

The temperature at which water turns to steam at sea level: 212 F or 100 C, the second anchor for the scales.

Absolute reference (-40)

The unique temperature where Fahrenheit and Celsius read the same number, minus 40 on both scales.

Gas mark

A UK oven-dial scale for gas cookers. Gas mark 4 is about 350 F or 175 C, and gas mark 6 is about 400 F or 200 C.

Degree

A single unit of temperature on a scale. A Fahrenheit degree is smaller than a Celsius degree, since 180 F degrees span the same range as 100 C degrees.

Frequently asked questions