🌡️ Celsius to Fahrenheit Converter (C to F, Both Ways)

What is the Celsius to Fahrenheit Converter?

Celsius and Fahrenheit are two different scales for measuring the same thing, temperature, and they simply place their zero points and their step sizes in different spots. The Celsius scale, used almost everywhere outside the United States, sets 0 degrees at the freezing point of water and 100 degrees at its boiling point at sea level, splitting that range into 100 equal degrees. The Fahrenheit scale, still standard for weather and cooking in the United States, puts water freezing at 32 degrees and boiling at 212 degrees, a span of 180 degrees. Because 180 Fahrenheit degrees cover the same physical range as 100 Celsius degrees, each Celsius degree is 180/100 = 9/5 = 1.8 times as wide as a Fahrenheit degree.

That 9/5 ratio is the whole reason the formula looks the way it does. To turn Celsius into Fahrenheit you first stretch the scale by multiplying by 9/5 so the degree sizes match, then you shift by adding 32 so the zero points line up, because water freezes at 0 in Celsius but at 32 in Fahrenheit. Written out, the exact relationship is F = C x 9/5 + 32. There is no rounding hidden in the factor: 9/5 is an exact fraction, so the conversion is precise for any value you enter.

Going the other direction just undoes those two steps in reverse order. You first remove the 32 degree offset, then shrink the scale back down by multiplying by 5/9, which gives C = (F - 32) x 5/9. A handy checkpoint is minus 40 degrees, the single temperature where both scales read exactly the same number: -40 C equals -40 F. If your conversion of that value does not come out to -40 on both sides, you know a step went wrong.

Most of the time rounding to a whole degree or one decimal place is plenty, since a weather forecast or an oven setting does not need more. Precision starts to matter for medical readings, laboratory work and engineering, where a fraction of a degree can change a decision. Keep full precision through the calculation and round only the final answer, exactly as this converter does internally, so small errors never pile up across several conversions.

When to use it

• Reading a weather forecast from a Celsius country while you are used to Fahrenheit, or the reverse when travelling, so you know whether to pack a coat.
• Following a recipe or oven setting written in the other scale, for example converting a 180 degree Celsius bake to 356 degrees Fahrenheit.
• Checking a body temperature or fever: 37 degrees Celsius is a normal 98.6 degrees Fahrenheit, and 38 degrees Celsius is 100.4 degrees Fahrenheit.
• Doing science, chemistry or physics homework where measurements are given in one scale but the answer is expected in the other.

How to use the Celsius to Fahrenheit Converter

1. Type the temperature you have into the Celsius box (it starts pre-filled with 20 as an example).
2. Read the converted value straight from the Fahrenheit box, which updates the moment you type.
3. To go the other way, type into the Fahrenheit box instead and read the Celsius result.
4. Use a preset button for a common value like freezing or body temperature, or press Clear to start over.

Formula & method

Worked examples

Celsius to Fahrenheit chart (common temperatures)

Quick mental math steps

Common mistakes to avoid

• Adding 32 before multiplying. Order matters. You must multiply the Celsius value by 9/5 first and add 32 last. Adding 32 first, as in (C + 32) x 9/5, gives a wrong, larger answer. For 20 C the correct result is 68 F, not the 93.6 F the wrong order produces.
• Rounding the 1.8 factor too early. The factor is the exact fraction 9/5, which equals 1.8 with no approximation. There is no need to round it, but rounding an intermediate result to a whole number before finishing the second step can shift the final answer by a degree or more.
• Mixing up the two directions. Celsius to Fahrenheit multiplies by 9/5 and adds 32; Fahrenheit to Celsius subtracts 32 and multiplies by 5/9. Using the wrong formula for your starting scale is the most common error. Check that a known value like 0 C lands on 32 F.
• Forgetting that below zero is normal. Temperatures can be negative on both scales, and a value can be positive on one scale while negative on the other. For example, 10 degrees Fahrenheit is about minus 12 degrees Celsius. Always keep the minus sign through the whole calculation.

Glossary

Celsius (C)

A temperature scale where water freezes at 0 degrees and boils at 100 degrees at sea level. Used in most of the world.

Fahrenheit (F)

A temperature scale where water freezes at 32 degrees and boils at 212 degrees. Standard for weather and cooking in the United States.

Degree

A single unit of temperature on a scale. A Celsius degree is 1.8 times as wide as a Fahrenheit degree.

Freezing point

The temperature at which water turns to ice, 0 degrees Celsius or 32 degrees Fahrenheit at normal pressure.

Boiling point

The temperature at which water turns to steam, 100 degrees Celsius or 212 degrees Fahrenheit at sea level.

Offset

The fixed number, 32, added or removed to line up the different zero points of the two scales.

Frequently asked questions