Temperature Conversion Calculator: °C, °F and K

A temperature conversion calculator converts a value between Celsius (°C), Fahrenheit (°F), and kelvin (K). Enter a temperature and choose its starting and target units to get the equivalent value, using the correct offset as well as scale.

Formula

The block converts the entered Celsius temperature to Fahrenheit and kelvin. The formulas are:

• Fahrenheit: °F = (°C × 9/5) + 32
• Kelvin: K = °C + 273.15

Here, °C is the input temperature in degrees Celsius, °F is the result in degrees Fahrenheit, and K is the result in kelvin. A kelvin is written K, without a degree symbol. These formulas convert temperature readings; they do not convert temperature differences in exactly the same way. A change of 1°C equals a change of 1.8°F, while a change of 1°C equals a change of 1 K.

Worked Example

For the default input of 20°C:

1. Convert to Fahrenheit: 20 × 9/5 + 32 = 36 + 32 = 68°F.
2. Convert to kelvin: 20 + 273.15 = 293.15 K.

The results, rounded to two decimal places as shown by the calculator, are 68.00°F and 293.15 K. The extra zero in 68.00°F reflects the display precision, not greater certainty in the original measurement.

How Temperature Conversion Works

Celsius and Fahrenheit use different-sized degrees and different zero points. Celsius sets 0°C at the freezing point of water under standard atmospheric pressure and 100°C at its boiling point under the same condition. Fahrenheit places those reference points at 32°F and 212°F. Since the Fahrenheit interval between them is 180 degrees and the Celsius interval is 100 degrees, each Celsius degree corresponds to 9/5 Fahrenheit degrees. The added 32 accounts for the different starting points.

Kelvin uses the same degree interval as Celsius but starts at absolute zero, the theoretical lower limit of thermodynamic temperature. That is why converting from Celsius to kelvin requires adding 273.15, not multiplying by a scale factor. For example, 0°C is 273.15 K, and absolute zero is 0 K, equivalent to −273.15°C.

Common reverse conversions are:

• Fahrenheit to Celsius: °C = (°F − 32) × 5/9
• Kelvin to Celsius: °C = K − 273.15
• Kelvin to Fahrenheit: °F = (K − 273.15) × 9/5 + 32
• Fahrenheit to kelvin: K = (°F − 32) × 5/9 + 273.15

When to Use a Temperature Converter

A calculator is useful when a recipe, weather report, science reference, appliance setting, or travel destination uses a different temperature scale from the one you know. It can also help check a manual or compare readings in a table. Use the scale conversion only: it does not account for differences between measuring devices, locations, or conditions.

For everyday readings, a decimal result may be more precise than the source warrants. If a thermometer reads approximately 20°C, reporting 68°F is usually more meaningful than reporting 68.0000°F. In scientific work, keep enough digits during intermediate calculations and round the final result to match the precision of the measurement and the requirements of the task.

Common Conversion Mistakes

• Forgetting the offset: Celsius and Fahrenheit are not related by multiplication alone. For °C to °F, multiply by 9/5 and then add 32.
• Using the wrong order: For °F to °C, subtract 32 before multiplying by 5/9.
• Confusing a reading with a temperature change: The 32-degree offset applies to readings, not differences. A rise of 10°C is a rise of 18°F, not 50°F.
• Adding 273 instead of 273.15: This is a rough approximation. Use 273.15 for standard Celsius-to-kelvin conversion.
• Writing kelvin incorrectly: The unit symbol is K, not °K. Celsius and Fahrenheit use degree symbols.

Temperature Scales and Their Limits

Celsius and Fahrenheit are common for weather and everyday temperatures, with which scale is used depending largely on location and context. Kelvin is common in scientific calculations, especially where absolute temperature matters. The scales express the same physical temperature, but their numerical values differ.

Temperature conversion does not tell you whether a particular reading is safe, suitable, or expected. For example, a converted oven setting does not guarantee an identical cooking result: ovens may vary, and recipes may be designed around a particular appliance and method. Likewise, converting a weather reading does not account for wind, humidity, or how a thermometer was positioned. Treat the result as a unit conversion, not an interpretation of the conditions.

At extreme temperatures, conversions remain mathematical, but the physical context matters. Kelvin cannot be negative in ordinary thermodynamic use; a negative kelvin result from a Celsius conversion signals an input below absolute zero and is not a physically meaningful equilibrium temperature. Celsius and Fahrenheit readings below zero are possible and do not imply that there is no heat at all.

Frequently Asked Questions

How do I convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5, then add 32. For example, 25°C × 9/5 + 32 = 77°F.

How do I convert Fahrenheit to Celsius?
Subtract 32 from the Fahrenheit value, then multiply by 5/9. For example, (68°F − 32) × 5/9 = 20°C.

What is 0°C in Fahrenheit and kelvin?
Zero degrees Celsius equals 32°F and 273.15 K.

What is room temperature in Celsius and Fahrenheit?
Room temperature has no single fixed value, but 20°C is a commonly used example and equals 68°F. The appropriate indoor temperature depends on the setting and purpose.

Why is a temperature difference converted differently from a temperature reading?
A reading includes the offset between scales, while a difference does not. Multiply a Celsius difference by 9/5 to get the equivalent Fahrenheit difference; do not add 32.

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in c | Temperature in Celsius | °C | 20
out f | Temperature in Fahrenheit | °F | c * 9 / 5 + 32 | 2
out k | Temperature in kelvin | K | c + 273.15 | 2