Convert a reading, not a temperature change
These scales place zero at different temperatures. A weather reading of 20 °C becomes 68 °F, but a rise of 20 Celsius degrees is a rise of 36 Fahrenheit degrees. The calculator treats your input as a reading; the offsets in the formulas would be wrong for a temperature difference.
Worked examples
Formula / Calculation Method
°C = (°F − 32) × 5/9
K = °C + 273.15
How to Use This Tool
- Enter a number using a period for decimals, for example 2.5.
- Choose the From and To units. The result and reference table update as you type.
- Use Swap to reverse the units while keeping your entered value, or Copy Result to save the conversion.
Common Use Cases
Limits and interpretation
The calculator rejects readings below 0 K (−273.15 °C or −459.67 °F). This is a conventional everyday temperature converter. It does not model specialized negative-temperature states, sensor calibration, oven behavior, or measurement uncertainty.
For a change in temperature, omit the offset: a 10 °C rise is an 18 °F rise and a 10 K rise. Results are rounded for display, so carry the unrounded value through intermediate calculations when precision matters.
Common conversions and worked examples
Choose a starting pair, then change the units as needed. The examples below explain how to interpret the result for a specific task.
Celsius to Fahrenheit
Multiply the Celsius reading by 9/5, then add 32. The addition accounts for different scale zero points. Use the calculator for a temperature reading; a rise or fall in temperature needs only the multiplication, without adding 32.
A temperature change uses a different calculation
If the temperature rises from 20 °C to 25 °C, it rises from 68 °F to 77 °F: the change is 9 °F, not 41 °F. Multiply the 5-degree Celsius difference by 9/5 and omit the offset. Readings below −273.15 °C are rejected as below absolute zero.
Fahrenheit to Celsius
Subtract 32 before multiplying by 5/9. Reversing that order produces a different answer, so the parentheses in the formula matter. Negative Fahrenheit readings are valid as long as the temperature is not below absolute zero.
Readings and differences are separate
A temperature drop of 18 Fahrenheit degrees is a drop of 10 Celsius degrees: 18 × 5/9 = 10. Do not subtract 32 when converting a difference. For a reading, the offset is required. The tool rejects values below −459.67 °F and displays up to 12 significant digits for valid results.
Celsius to Kelvin
Celsius and kelvin use equal-sized increments, but start at different zero points. Add 273.15 to a Celsius reading to obtain kelvin. Write the result with K, without a degree sign; a Celsius-to-kelvin reading conversion does not use a multiplication factor.
Use absolute temperatures when a formula requires them
When an equation explicitly requires thermodynamic temperature in kelvin, convert the Celsius reading before substitution. For a change in temperature, however, a 5 °C difference already equals a 5 K difference; adding 273.15 to a difference is incorrect. The lowest accepted reading is −273.15 °C, which gives 0 K.
Kelvin to Celsius
Kelvin is an absolute temperature scale whose conventional lower boundary is 0 K. Subtract 273.15 to express the reading in Celsius. Values below 273.15 K become negative Celsius readings; that is expected and does not indicate an invalid conversion.
Check what the kelvin label describes
A laboratory temperature reading and a lamp's correlated color-temperature rating have different meanings. For a light labeled 3000 K, arithmetic gives 2726.85 °C, but that does not describe the lamp's surface temperature. Use the light's K rating to compare its color appearance, not to infer how hot it is.
A difference of 10 K is a difference of 10 °C. Do not subtract 273.15 from a temperature change.