The basic formula: multiply by 9, divide by 5, then add 32

To convert a temperature from Celsius to Fahrenheit, take the Celsius number, multiply it by 9, divide the result by 5, then add 32. That final number is the Fahrenheit temperature.

The formula written out is: (°C × 9/5) + 32 = °F

For example: if the temperature is 20°C, multiply 20 by 9 to get 180. Divide 180 by 5 to get 36. Add 32 to get 68°F. A 20°C day is a 68°F day. This same process works for any Celsius temperature, whether it is below zero or above 100.

You do not need to memorize the formula — you can write it down, keep it on your phone, or look it up each time. The important part is understanding the order of operations: multiply first, divide second, add 32 last. Doing the steps out of order will give you the wrong answer.

Key Takeaways

  • The conversion formula is (°C × 9/5) + 32 = °F, and you can do it on any calculator or by hand.
  • Multiply the Celsius temperature by 1.8 as a shortcut instead of multiplying by 9 and dividing by 5.
  • Zero degrees Celsius equals 32°F, and 100°C equals 212°F — the freezing and boiling points of water.
  • Most phones have a built-in calculator app that can handle the math, or you can search "convert [number] Celsius to Fahrenheit" online.
  • Memorizing a few anchor temperatures like 20°C = 68°F and 30°C = 86°F lets you estimate conversions without calculating every time.

Using the shortcut: multiply by 1.8, then add 32

If you want to skip a step, multiply the Celsius temperature by 1.8 instead of doing 9 divided by 5 separately. Then add 32 to that result.

The shortcut formula is: (°C × 1.8) + 32 = °F

Using the same example: 20°C times 1.8 equals 36. Add 32 to get 68°F. The answer is the same, and the math is slightly faster by hand. The reason this works is that 9 divided by 5 equals 1.8, so you are doing the same calculation in fewer steps.

The shortcut is especially useful if you convert temperatures regularly. Once you get used to multiplying by 1.8, you can do it faster than breaking it into two separate operations.

Common reference temperatures to remember

Knowing a few key temperatures makes it easier to estimate without calculating every time. Water freezes at 0°C, which is 32°F. Water boils at 100°C, which is 212°F. Room temperature is around 20°C or 68°F. A hot day might be 30°C, which is 86°F.

Body temperature is approximately 37°C, or about 98.6°F. A cold day might be 10°C, which is 50°F. If you remember these anchors, you can mentally estimate temperatures in between without pulling out a calculator. For instance, if someone tells you it is 25°C outside, you know it is somewhere between 68°F and 86°F — warmer than room temperature but not hot.

Converting in the other direction: Fahrenheit to Celsius

If you need to go the opposite way, subtract 32 from the Fahrenheit temperature first, then multiply by 5 and divide by 9. Or use the shortcut: subtract 32, then multiply by 0.556.

The formula is: (°F − 32) × 5/9 = °C

For example: 68°F minus 32 is 36. Multiply 36 by 5 to get 180. Divide by 9 to get 20°C. The shortcut would be: 68 minus 32 equals 36, times 0.556 equals 20°C. Notice that this formula reverses the Celsius-to-Fahrenheit process — you subtract 32 instead of adding it, and you multiply by 5/9 instead of 9/5.

Using your phone or computer to convert

You do not have to do the math yourself. Open the calculator app on your phone, enter the Celsius temperature, and perform the calculation. Most calculators have a clear display and let you see each step as you go.

You can also type the conversion directly into a search engine. Search "25 Celsius to Fahrenheit" and the result appears instantly. This method works on any device with internet access and removes the chance of arithmetic error. Many weather apps also let you toggle between Celsius and Fahrenheit in the settings, so if you use weather information regularly, you can set it to whichever scale you prefer.

Why the formula works this way

Celsius and Fahrenheit use different starting points and different sized degrees. Celsius sets 0 at the freezing point of water and 100 at the boiling point. Fahrenheit sets 32 at freezing and 212 at boiling. That means Fahrenheit degrees are smaller — it takes 1.8 Fahrenheit degrees to equal one Celsius degree.

The formula accounts for both the different scale size (the 1.8 multiplier) and the different starting point (the 32 added at the end). Understanding this is not necessary to convert, but it explains why the numbers work the way they do. The two scales are measuring the same thing — heat — but they divide the range differently and start counting from different points.

Frequently Asked Questions

What is 0 degrees Celsius in Fahrenheit?

Zero degrees Celsius is 32°F. This is the freezing point of water. Using the formula: (0 × 1.8) + 32 = 32°F. This is one of the most useful reference points to remember because it comes up often in weather and cooking.

What is 37 degrees Celsius in Fahrenheit?

37°C is approximately 98.6°F, which is normal human body temperature. Using the formula: (37 × 1.8) + 32 = 98.6°F. This temperature is useful to know if you are reading a thermometer or checking someone's fever.

Is there a way to convert without doing math?

Yes. Use your phone's calculator app or search the conversion online. You can also memorize common temperatures like 20°C = 68°F, 30°C = 86°F, and 0°C = 32°F to estimate without calculating. Over time, if you convert regularly, you will start to recognize patterns and can estimate more quickly.

Why do some countries use Celsius and others use Fahrenheit?

Celsius is the standard in most countries and in science worldwide. Fahrenheit is used primarily in the United States, some Caribbean nations, and a few other places. The choice is historical — Fahrenheit was developed first, but Celsius became the international standard because it aligns with the freezing and boiling points of water.

Can I convert negative Celsius temperatures?

Yes, the formula works the same way. For example, −10°C converts to (−10 × 1.8) + 32 = 14°F. Negative Celsius temperatures are common in cold climates, and the conversion process does not change — you still multiply by 1.8 and add 32.