Temperature Converter
Convert between Celsius, Fahrenheit and Kelvin with the correct formulas.
The temperature converter switches between Celsius, Fahrenheit and Kelvin. Unlike length or weight, temperature scales have different zero points, so these conversions use formulas rather than simple multipliers.
How to use the converter
- Enter the temperature value.
- Choose the scale you have and the scale you want.
- The result is exact, using the standard conversion formulas.
- All three scales are shown in the conversion table.
How the conversion works
K = °C + 273.15 · °C = K − 273.15
Worked example
25 °C to Fahrenheit
°F = 25 × 9 ÷ 5 + 32 = 77 °F
The same temperature is 298.15 K.
Popular conversions
Jump straight to a single conversion, or use the converter above for any pair.
Who should use this temperature converter
- Travellers checking a weather forecast, an oven setting or a fridge temperature in the other scale.
- Cooks following a recipe written in Fahrenheit while their oven is marked in Celsius.
- Students working through thermodynamics, where Kelvin is the scale that actually matters.
- Anyone monitoring a fever, an aquarium, a freezer or a workshop, where an exact conversion avoids a costly mistake.
Common mistakes to avoid
- Converting a temperature difference as if it were a temperature. A rise of 10°C is a rise of 18°F — you scale by 9/5 and do not add 32. Adding 32 to a difference is one of the most common errors in heating and engineering work.
- Getting the order wrong going from Fahrenheit. Subtract 32 first, then multiply by 5 and divide by 9. Multiplying before subtracting gives an answer that is wrong by a wide margin.
- Assuming Kelvin can be negative. Kelvin starts at absolute zero, so it has no negative values. Celsius and Fahrenheit both do.
- Mixing up oven temperature and cooking time. A 25°C difference in oven temperature changes how a bake rises, so convert the setting carefully and expect to adjust the time.
- Treating a fever reading casually. 100.4°F is exactly 38°C, the usual threshold for a fever. Rounding is fine for the weather, not for health decisions.
Three scales and three zero points
Celsius and Fahrenheit are relative scales with arbitrary zero points — the freezing point of water and a historical brine mixture. Kelvin is an absolute scale that starts at absolute zero, the point at which molecular motion essentially stops. That is why science uses Kelvin: ratios and gas laws only behave sensibly when zero really means zero.
The two relative scales cross at exactly −40 degrees, the only temperature where Celsius and Fahrenheit read the same number. Useful anchors to remember: 0°C is 32°F, 37°C is 98.6°F, and 100°C is 212°F. For everyday conversions, each Celsius degree equals 1.8 Fahrenheit degrees, which is why a 5°C change feels like a 9°F change.
Temperature terms explained
- Celsius
- The scale used across most of the world, with water freezing at 0°C and boiling at 100°C at sea level.
- Fahrenheit
- Used mainly in the United States, with water freezing at 32°F and boiling at 212°F.
- Kelvin
- The SI base unit of temperature, starting at absolute zero and using degrees the same size as Celsius.
- Absolute zero
- The lowest possible temperature, 0 K or −273.15°C, at which particles have minimum energy.
- Temperature interval
- A difference between two temperatures. Intervals convert differently from absolute readings, using only the 9/5 factor.
Everyday temperature anchors
Knowing a handful of reference points makes conversion unnecessary in most daily situations. Normal body temperature is 37°C or 98.6°F, and a fever threshold of 38°C is 100.4°F. A comfortable room sits between 20 and 24°C, which is 68 to 75°F. A fridge should hold about 4°C — 39°F — and a freezer −18°C, or 0°F.
In the kitchen, a moderate oven at 180°C is 356°F, a hot oven at 220°C is 428°F, and water boils at 100°C or 212°F at sea level. At altitude, water boils below 100°C, which is why cooking times lengthen in the hills. These anchors cover almost every everyday case without needing a calculator at all.
Frequently asked questions
How do I convert Celsius to Fahrenheit?
Multiply by 9, divide by 5, then add 32. So 25 °C becomes 25 × 9 ÷ 5 + 32 = 77 °F. To go from Fahrenheit to Celsius, subtract 32 first, then multiply by 5 and divide by 9.
At what temperature are Celsius and Fahrenheit equal?
At −40 degrees. That is the only point where both scales read the same number: −40 °C = −40 °F.
How do I convert Celsius to Kelvin?
Add 273.15 to the Celsius value. So 25 °C is 298.15 K. Kelvin is the scientific scale and starts at absolute zero, so it has no negative values.