Celsius to Fahrenheit Formula: How to Convert (With Tricks)

To convert Celsius to Fahrenheit, multiply the Celsius value by 9/5 (which is the same as multiplying by 1.8) and then add 32. Written as a formula: F = (C × 1.8) + 32. That single equation covers every temperature conversion you will ever need, from checking the weather to reading an oven recipe. Below you will find the formula explained step by step with worked examples, the reverse formula for going from Fahrenheit back to Celsius, a quick mental-math trick that works without a calculator, and a reference table of the most useful temperatures in both scales.

The two scales are used in different parts of the world, which makes conversion a genuinely practical skill. Most countries use Celsius for everyday temperature, while the United States uses Fahrenheit. Anyone who cooks with recipes from another country, checks international weather, or reads scientific and medical information encounters both scales regularly.

The Celsius to Fahrenheit formula explained

The formula has two parts: a multiplication and an addition. Written in full:

• Step 1: Multiply the Celsius temperature by 1.8 (or 9 divided by 5).
• Step 2: Add 32 to the result.

The multiplication step rescales the temperature because the two scales use different sized degrees. One Celsius degree is larger than one Fahrenheit degree: a span of 100 degrees in Celsius covers the same range as 180 degrees in Fahrenheit, which gives the ratio of 9/5 or 1.8. The addition of 32 shifts the result because the two scales have different zero points. Fahrenheit sets its zero below the freezing point of water, while Celsius sets zero exactly at the freezing point.

Worked examples: Celsius to Fahrenheit

Here are four common temperatures worked through the formula so you can see how each step plays out.

• 0 C (freezing point of water): (0 × 1.8) + 32 = 0 + 32 = 32 F.
• 20 C (a comfortable room): (20 × 1.8) + 32 = 36 + 32 = 68 F.
• 37 C (normal body temperature): (37 × 1.8) + 32 = 66.6 + 32 = 98.6 F.
• 100 C (boiling point of water): (100 × 1.8) + 32 = 180 + 32 = 212 F.

Notice that the formula produces exact, round answers at the key reference points. That is not a coincidence: those reference points were the anchors used when the Celsius scale was defined. For temperatures in between, the result is usually a decimal, and rounding to one decimal place is more than precise enough for everyday use.

The reverse formula: Fahrenheit to Celsius

To go the other direction, reverse the two operations. Start by subtracting 32, then multiply by 5/9 (which is the same as dividing by 1.8):

• Step 1: Subtract 32 from the Fahrenheit temperature.
• Step 2: Multiply the result by 5/9 (or divide by 1.8).

Written as a formula: C = (F − 32) × 5/9.

• 32 F: (32 − 32) × 5/9 = 0 × 5/9 = 0 C.
• 77 F: (77 − 32) × 5/9 = 45 × 0.5556 = 25 C.
• 98.6 F: (98.6 − 32) × 5/9 = 66.6 × 0.5556 = 37 C.
• 212 F: (212 − 32) × 5/9 = 180 × 0.5556 = 100 C.

The reverse formula is used constantly in cooking. A recipe might call for an oven at 180 C, a Fahrenheit oven owner needs to know that is 356 F, which they would round up to 350 F or 375 F on a standard dial. For a full set of oven conversions, see the oven temperature conversion chart.

The mental-math trick: double and add 30

The exact formula requires a calculator for most temperatures, but there is a faster approximation that works well in everyday situations. The trick is to double the Celsius value and add 30:

• Take the Celsius temperature.
• Multiply by 2 (double it).
• Add 30.

For example, 22 C becomes (22 × 2) + 30 = 44 + 30 = 74 F. The exact answer is 71.6 F, so the estimate is about 2 degrees high. That level of accuracy is perfectly fine for understanding a weather forecast, deciding what to wear, or estimating how warm a room feels. The trick is most reliable in the everyday range of about 0 C to 30 C. At extreme temperatures, the error grows because 30 is only an approximation of 32, and doubling approximates multiplying by 1.8 rather than 2. For anything precise, such as medical temperatures or oven settings, use the exact formula or the converter below.

Here is a quick comparison of the trick versus the exact formula across a few common temperatures:

The trick hits exactly at 10 C (50 F) and stays within a few degrees across the range most people encounter outdoors. Notice that at body temperature (37 C) the error reaches about 5 degrees, which is why the trick should not be used for medical readings.

Reference table: common temperatures in Celsius and Fahrenheit

The table below covers the temperatures that come up most often in daily life, from the freezing point of water through cooking and oven temperatures. Memorizing even a handful of these anchors makes the formula much easier to use in practice.

The minus 40 entry is worth a second look. It is the one temperature where you do not need to convert at all, because both scales read the same number. This happens because the formulas for the two scales cross exactly at that point: (minus 40 × 1.8) + 32 = minus 72 + 32 = minus 40.

Why do two temperature scales exist?

The Fahrenheit scale was created by German physicist Daniel Gabriel Fahrenheit in 1724. He set his zero point using a brine solution of ice, water, and ammonium chloride, which was roughly the coldest temperature he could reliably reproduce in a lab. He then set 96 degrees as human body temperature, placing the freezing and boiling points of water at 32 and 212 degrees. The scale was practical for its time and became standard in Britain and its colonies, including what would become the United States.

The Celsius scale was proposed by Swedish astronomer Anders Celsius in 1742. It set zero at the freezing point of water and 100 at the boiling point at standard atmospheric pressure. The clean 0 to 100 structure made it straightforward to understand and calculate with, and it became part of the metric system when the international scientific community standardised units in the 19th century. Today, almost every country uses Celsius for official and everyday temperatures, with the United States being the most prominent exception.

The practical result is that anyone interacting with both American and international content regularly needs to move between the two scales. International recipes almost always give oven temperatures in Celsius. Weather apps often let you toggle between scales. Medical research and scientific literature use Celsius or its close relative, Kelvin, exclusively. Knowing the formula means you are never stuck.

Tips for remembering the formula

The formula is not hard to memorise if you anchor it to the two facts you probably already know: water freezes at 0 C and 32 F, and water boils at 100 C and 212 F. The gap between freezing and boiling is 100 degrees in Celsius and 180 degrees in Fahrenheit. The ratio 180 to 100 simplifies to 9 to 5, which is where the 9/5 in the formula comes from. The 32 is just the offset to account for the different zero points. If you can recall those two reference temperatures, you can reconstruct the formula from scratch any time you need it.

• Celsius to Fahrenheit: multiply by 1.8 (or 9/5), then add 32. F = (C × 1.8) + 32.
• Fahrenheit to Celsius: subtract 32, then multiply by 5/9 (or divide by 1.8). C = (F − 32) × 5/9.
• Quick mental estimate: double the Celsius value and add 30. Accurate within a few degrees for everyday temperatures.