To convert Celsius to Fahrenheit, multiply by 9/5 (1.8) and add 32. To convert Fahrenheit to Celsius, subtract 32 and multiply by 5/9. Kelvin is Celsius plus 273.15. Our free temperature converter does all three directions instantly, including negative temperatures.
The formulas look different because the scales differ in two ways: where zero sits and how big one degree is. Once you see that, every Celsius to Fahrenheit conversion makes sense, and so does the most common mistake people make with them.
Celsius, Fahrenheit and Kelvin compared
- Celsius (°C) puts the freezing point of water at 0 °C and the boiling point at 100 °C, at standard sea-level pressure. Most countries use it for weather, cooking and medicine.
- Fahrenheit (°F) puts the same two points at 32 °F and 212 °F, so they are 180 degrees apart instead of 100. It is the everyday scale in the United States and a handful of other countries and territories.
- Kelvin (K) starts at absolute zero, the lowest possible temperature, and uses degrees the same size as Celsius. Scientists use it because it has no negative values. It is written without a degree sign: 300 K, not 300 °K.
Because 100 Celsius degrees span the same range as 180 Fahrenheit degrees, one Celsius degree equals 1.8 Fahrenheit degrees. That ratio is where 9/5 comes from, and the 32 accounts for the different zero points.
Temperature reference points
| Reference point | Celsius | Fahrenheit | Kelvin |
|---|---|---|---|
| Absolute zero | −273.15 °C | −459.67 °F | 0 K |
| Celsius and Fahrenheit match | −40 °C | −40 °F | 233.15 K |
| Water freezes | 0 °C | 32 °F | 273.15 K |
| Typical room temperature | 20 °C | 68 °F | 293.15 K |
| Average body temperature (traditional value) | 37 °C | 98.6 °F | 310.15 K |
| Water boils at sea level | 100 °C | 212 °F | 373.15 K |
| Moderate oven | 180 °C | 356 °F | 453.15 K |
Temperature conversion formulas
°F = °C × 9/5 + 32
°C = (°F - 32) × 5/9
K = °C + 273.15
°C = K - 273.15
°F = (K - 273.15) × 9/5 + 32Worked example: Celsius to Fahrenheit
Convert 25 °C to Fahrenheit:
- Multiply by 9/5: 25 × 1.8 = 45.
- Add 32: 45 + 32 = 77 °F.
Worked example: Fahrenheit to Celsius
Convert an oven setting of 350 °F to Celsius:
- Subtract 32: 350 − 32 = 318.
- Multiply by 5/9: 318 × 5 ÷ 9 = 176.67 °C.
Recipes usually round this to 180 °C. For oven work, the oven temperature converter also handles gas marks, and our oven temperature conversion guide goes into more detail.
Worked example: Kelvin to Celsius and Fahrenheit
Convert 300 K: subtract 273.15 to get 26.85 °C, then 26.85 × 1.8 + 32 = 80.33 °F.
Celsius to Fahrenheit chart for everyday temperatures
| Celsius | Fahrenheit | Feels like |
|---|---|---|
| −10 °C | 14 °F | Hard frost |
| 0 °C | 32 °F | Freezing |
| 10 °C | 50 °F | Cool, jacket weather |
| 15 °C | 59 °F | Mild |
| 20 °C | 68 °F | Room temperature |
| 25 °C | 77 °F | Warm |
| 30 °C | 86 °F | Hot |
| 35 °C | 95 °F | Very hot |
| 40 °C | 104 °F | Extreme heat |
A mental shortcut that is close enough for weather
Double the Celsius figure and add 30. For 20 °C that gives 70 °F (exact: 68 °F). For the reverse, subtract 30 from Fahrenheit and halve it. The shortcut drifts at the extremes: 35 °C comes out as 100 °F when the real answer is 95 °F, so use the exact formula for cooking, science or health.
How to use the Temperature Converter
- Open the Temperature Converter. It starts at 0 Celsius to Fahrenheit, which shows 32.
- Type the reading in the Value field. Negative numbers and decimals are accepted, so −40 or 98.6 both work.
- Select the scale you are starting from in the From list: Celsius, Fahrenheit or Kelvin.
- Select the target scale in the To list.
- Read the Result, rounded to two decimal places. It updates as you type.
- Press the swap button to reverse the direction without retyping the value.
Common temperature conversion mistakes
- Converting a temperature change as if it were a reading. A rise of 10 °C is a rise of 18 °F, not 50 °F. The +32 only applies to actual readings. For a difference, multiply by 1.8 and skip the 32. The converter converts readings, so do differences by hand.
- Adding 32 before multiplying. Order matters. 25 °C becomes (25 × 1.8) + 32 = 77 °F; adding first gives (25 + 32) × 1.8 = 102.6 °F, which is wrong.
- Writing "degrees Kelvin". The unit is the kelvin, symbol K, with no degree sign.
- Using 273 instead of 273.15. Fine for a rough answer, but it adds a 0.15 degree error that matters in lab work.
- Treating 98.6 °F as a fixed rule. It is a traditional average. Normal body temperature varies between people and through the day, so follow medical guidance rather than a single number.
Temperature also matters in the kitchen beyond the oven dial. Our cooking converter handles the cups-to-grams side of a recipe, and the guide to precision cooking conversions explains why accurate measures matter.
Frequently asked questions
What is the formula to convert Celsius to Fahrenheit?
Multiply the Celsius temperature by 1.8 (or 9/5) and add 32. For example, 30 °C × 1.8 + 32 = 86 °F.
How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit temperature, then multiply by 5/9. For example, (68 − 32) × 5/9 = 20 °C.
At what temperature are Celsius and Fahrenheit the same?
The two scales meet at −40. At that point −40 °C and −40 °F describe exactly the same temperature.
What is 180 °C in Fahrenheit?
180 °C is 356 °F. Recipes usually round it to 350 °F, which is 176.67 °C.
Why do scientists use Kelvin instead of Celsius?
Kelvin starts at absolute zero, so it has no negative values and 200 K is genuinely twice the absolute temperature of 100 K. That makes it the natural unit for gas laws, thermodynamics and other physics formulas.
Can a Kelvin temperature be negative?
No. Zero kelvin is absolute zero, the lowest possible temperature, so the Kelvin scale has no negative values.