Temperature Degrees Calculator: Convert °C, °F and K

A temperature degrees calculator converts a reading between Celsius (°C), Fahrenheit (°F), and kelvin (K). Enter a value and choose its starting and destination scales to get the equivalent temperature, with the conversion formula shown below.

Formula

The calculator takes one temperature reading, converts it to a common scale, and expresses that value on the selected destination scale. The available relationships are:

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

Here, the input temperature is the number you enter, in the unit selected as the starting scale. The output is the equivalent number in the destination unit. The long expression in the calculator block selects the appropriate relationship based on the two drop-down choices; the equations above are the clearer forms to use when doing a conversion by hand.

Worked Example

With the defaults, the input is 20 °C, the starting scale is Celsius, and the destination is Fahrenheit. Apply the Celsius-to-Fahrenheit equation:

°F = (20 × 9/5) + 32 = 36 + 32 = 68 °F.

The result is 68.00 °F. This agrees with the calculator output rounded to two decimal places. To convert the same reading to kelvin instead, use K = 20 + 273.15 = 293.15 K.

How the Temperature Scales Work

Celsius and Fahrenheit are everyday temperature scales, but their degree intervals differ. A change of 1 °C is equal to a change of 1.8 °F. Their zero points also differ: 0 °C is 32 °F, so converting between them requires both a scale adjustment and an offset.

Kelvin is the SI base unit for thermodynamic temperature. Its steps have the same size as Celsius degrees, but the scales start at different points: 0 K is absolute zero, equivalent to −273.15 °C. Kelvin values are written without a degree sign: 300 K, not 300 °K. The kelvin scale is not limited to ordinary weather or room temperatures, so the conversion formula should not be mistaken for a range of temperatures people commonly encounter.

When to Use a Temperature Converter

A converter is useful when a reading is given in a different scale from the one needed for a report, school exercise, recipe, weather comparison, or instrument display. Always identify both the number and its unit before calculating. A reading of 20 could mean 20 °C, 20 °F, or 20 K, and those are not interchangeable.

• Use Celsius-to-Fahrenheit for comparing many international weather reports with US forecasts.
• Use Fahrenheit-to-Celsius when adapting a temperature value stated in Fahrenheit to a Celsius-based context.
• Use Celsius-to-kelvin or kelvin-to-Celsius for scientific quantities that require the SI temperature scale.

For a temperature difference rather than a specific reading, the offset cancels. For example, a rise of 10 °C is a rise of 18 °F; it is not 50 °F. In kelvin, a change of 10 K has the same size as a change of 10 °C.

Common Conversion Mistakes

The most frequent error is applying the multiplication but forgetting the offset. Converting Celsius to Fahrenheit is not just multiplying by 9/5: 20 °C × 9/5 is 36, but the correct result is 68 °F after adding 32. In the reverse direction, subtract 32 before multiplying by 5/9.

• Do not treat Celsius and Fahrenheit degrees as equal-sized intervals.
• Do not add 273.15 to a Fahrenheit number directly; first convert Fahrenheit to Celsius, or use the combined formula.
• Keep the input unit and selected starting scale consistent. A number entered as Fahrenheit but marked Celsius will produce a mathematically valid, unintended conversion.
• Round only at the end. Intermediate rounding can shift the last digit, especially in conversions involving Fahrenheit.
• Distinguish a temperature from a temperature change: offsets apply to readings, not to differences.

Precision and Limits

The displayed result is rounded to two decimal places, but the equations use the entered value rather than a rounded intermediate answer. The decimal places shown do not guarantee that the original measurement was that precise. A thermometer reading of 20 °C with uncertainty of about one degree does not become a highly precise measurement merely because its converted value is written as 68.00 °F.

The calculator accepts Celsius inputs down to −273.15 °C, corresponding to 0 K, and has no upper input limit. This is a mathematical converter, not a test of whether a stated measurement is physically achievable under a particular set of conditions. In practical measurement, instrument range, calibration, resolution, and uncertainty matter too.

Frequently Asked Questions

How do you convert Celsius to Fahrenheit?
Multiply the Celsius value by 9/5, then add 32. For example, 20 °C becomes (20 × 9/5) + 32 = 68 °F.

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

How do you convert Celsius to kelvin?
Add 273.15 to the Celsius value. Thus, 20 °C equals 293.15 K. Write kelvin with K, not °K.

Is a degree Celsius the same size as a degree Fahrenheit?
No. A change of 1 °C equals a change of 1.8 °F. Celsius and kelvin have equally sized increments, although their zero points differ.

What is 0 °C in Fahrenheit and kelvin?
Zero Celsius is 32 °F and 273.15 K. It is not absolute zero; absolute zero is 0 K, or −273.15 °C.

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in t | Temperature | °C | 20 | -273.15
sel s | Convert from | Celsius=1, Fahrenheit=2, Kelvin=3
sel d | Convert to | Fahrenheit=1, Celsius=2, Kelvin=3
out result | Converted temperature | °C, °F, or K | (t + 273.15) * (1 - (s - 1) * (s - 2) / 2) * (1 - (d - 1) * (d - 2) / 2) + ((t - 32) * 5 / 9 + 273.15) * (s - 1) * (1 - (s - 2) * (s - 3) / 2) * (1 - (d - 1) * (d - 2) / 2) + (t - 273.15) * (s - 1) * (s - 2) / 2 * (1 - (d - 1) * (d - 2) / 2) + ((t + 273.15) * 9 / 5 + 32) * (1 - (s - 1) * (s - 2) / 2) * (d - 1) * (1 - (d - 1) * (d - 2) / 2) + (t * 9 / 5 + 32) * (s - 1) * (1 - (s - 2) * (s - 3) / 2) * (d - 1) * (1 - (d - 1) * (d - 2) / 2) + ((t - 273.15) * 9 / 5 + 32) * (s - 1) * (s - 2) / 2 * (d - 1) * (1 - (d - 1) * (d - 2) / 2) + t + (s - 1) * (s - 2) * (d - 1) * (d - 2) / 4 | 2