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Temperature Conversion Overview
The Temperature Conversion tool converts instantly between Celsius, Fahrenheit, Kelvin, and Rankine. Enter a temperature in one unit and the calculator returns the equivalent values in the other temperature scales.
Temperature conversion is used in electronics, thermal design, HVAC work, laboratory measurement, manufacturing, and everyday unit conversion. In engineering, it is especially important to distinguish between an actual temperature and a temperature difference, because Celsius and Fahrenheit use offsets while kelvin and Rankine are absolute scales.
Supported Temperature Units
| Unit | Symbol | Scale Type | Common Use |
|---|---|---|---|
| Celsius | °C | Offset scale | General temperature measurement, science, weather, and industry |
| Fahrenheit | °F | Offset scale | Common everyday temperature scale in the United States |
| Kelvin | K | Absolute scale | SI thermodynamic temperature, science, physics, and engineering |
| Rankine | °R | Absolute scale | Engineering calculations based on Fahrenheit-size degrees |
What Is Celsius?
Celsius is a temperature scale expressed in degrees Celsius, symbol °C. The degree Celsius has the same size as the kelvin, but the Celsius scale is offset from the Kelvin scale by 273.15. This relationship is:
°C = K - 273.15
Because Celsius is an offset scale, it is suitable for everyday temperatures, but it is not an absolute ratio scale. For example, 40 °C is not twice as much thermodynamic temperature as 20 °C.
What Is Fahrenheit?
Fahrenheit is a temperature scale expressed in degrees Fahrenheit, symbol °F. On this scale, water freezes at about 32 °F and boils at about 212 °F at standard atmospheric pressure, so the interval between those reference points is 180 Fahrenheit degrees.
Fahrenheit is also an offset scale. It is often used for weather, room temperature, cooking, and industrial specifications in regions where inch-pound units are common.
What Is Kelvin?
Kelvin, symbol K, is the SI base unit of thermodynamic temperature. It is an absolute temperature scale that starts at absolute zero. A temperature change of 1 K is equal in size to a temperature change of 1 °C.
Kelvin values are commonly used in physics, thermodynamics, semiconductor calculations, noise analysis, LED color temperature, and many engineering formulas where absolute temperature is required.
What Is Rankine?
Rankine, symbol °R, is an absolute temperature scale that uses the same interval size as the Fahrenheit degree. In the same way that kelvin is the absolute-temperature partner of Celsius, Rankine is the absolute-temperature partner of Fahrenheit.
Absolute zero is 0 K and 0 °R. The relationship between Rankine and Fahrenheit is:
°R = °F + 459.67
Temperature Conversion Formulas
| Convert From | Convert To | Formula |
|---|---|---|
| Fahrenheit | Celsius | °C = (°F - 32) × 5 / 9 |
| Celsius | Fahrenheit | °F = (°C × 9 / 5) + 32 |
| Celsius | Kelvin | K = °C + 273.15 |
| Kelvin | Celsius | °C = K - 273.15 |
| Fahrenheit | Kelvin | K = (°F + 459.67) × 5 / 9 |
| Kelvin | Fahrenheit | °F = (K × 9 / 5) - 459.67 |
| Fahrenheit | Rankine | °R = °F + 459.67 |
| Rankine | Fahrenheit | °F = °R - 459.67 |
| Kelvin | Rankine | °R = K × 9 / 5 |
| Rankine | Kelvin | K = °R × 5 / 9 |
Common Temperature Reference Points
| Reference Point | Celsius | Fahrenheit | Kelvin | Rankine |
|---|---|---|---|---|
| Absolute zero | -273.15 °C | -459.67 °F | 0 K | 0 °R |
| Water freezing point | 0 °C | 32 °F | 273.15 K | 491.67 °R |
| Typical room temperature | 20 °C | 68 °F | 293.15 K | 527.67 °R |
| Water boiling point at 1 atm | 100 °C | 212 °F | 373.15 K | 671.67 °R |
The freezing and boiling points of water depend on pressure and water purity, so they are best treated as practical reference points rather than the modern definition of the Celsius scale.
Temperature Difference vs. Temperature Value
A temperature difference does not always use the same conversion as a temperature value. For example, a change of 10 °C equals a change of 18 °F, but 10 °C as an actual temperature equals 50 °F.
| Temperature Interval | Equivalent Interval |
|---|---|
| 1 °C difference | 1 K difference |
| 1 °C difference | 1.8 °F difference |
| 1 K difference | 1.8 °R difference |
| 1 °F difference | 1 °R difference |
Example Temperature Conversions
| Input | Calculation | Result |
|---|---|---|
| 25 °C to °F | (25 × 9 / 5) + 32 | 77 °F |
| 77 °F to °C | (77 - 32) × 5 / 9 | 25 °C |
| 25 °C to K | 25 + 273.15 | 298.15 K |
| 77 °F to °R | 77 + 459.67 | 536.67 °R |
| 300 K to °C | 300 - 273.15 | 26.85 °C |
How to Use the Temperature Conversion Tool
Choose the temperature unit you already know.
Enter the value in the matching input field.
Read the converted values in Celsius, Fahrenheit, Kelvin, and Rankine.
Use the reset function before starting a separate conversion if the tool provides one.
For physical temperature values, Kelvin and Rankine should not be negative because both scales begin at absolute zero.
Common Mistakes to Avoid
| Mistake | Why It Matters | Better Practice |
|---|---|---|
| Using °C + 273 instead of °C + 273.15 | The result is rounded and may be unsuitable for precise work. | Use 273.15 unless a rough estimate is acceptable. |
| Writing °K for kelvin | The SI symbol is K, not °K. | Write 300 K, not 300 °K. |
| Confusing temperature values with temperature differences | Offset scales require different handling for actual values and intervals. | Use interval conversions for temperature rise or drop. |
| Using Celsius in formulas that require absolute temperature | Thermodynamic formulas often require K or °R. | Convert to kelvin or Rankine before calculating. |
Applications
Temperature conversion is useful when comparing datasheet limits, calculating thermal resistance, estimating junction temperature, converting oven or reflow profiles, working with HVAC specifications, interpreting sensor readings, and converting laboratory measurements.
In electronics, many calculations use Celsius for operating ranges and kelvin for absolute-temperature formulas. For example, semiconductor behavior, thermal noise, and some physics-based models require absolute temperature.
FAQ
What is the SI unit of temperature?
The SI base unit of thermodynamic temperature is the kelvin, symbol K.
Is Celsius the same size as kelvin?
Yes. A temperature change of 1 °C is equal in size to a temperature change of 1 K, but the zero points are different.
Why does Fahrenheit use 32 in the formula?
Fahrenheit is an offset scale. The value 32 accounts for the offset between the Fahrenheit and Celsius zero points.
What is absolute zero?
Absolute zero is the zero point of thermodynamic temperature. It is 0 K, -273.15 °C, -459.67 °F, and 0 °R.
When should I use Kelvin instead of Celsius?
Use kelvin when a formula depends on absolute temperature, such as thermodynamics, gas laws, thermal noise, and many physics-based calculations.
