Convert the reading, including its sign
A reading of −10 °C is a temperature below zero on the Celsius scale. It is not a negative amount of heat, and converting it does not remove the minus sign by taking an absolute value. Enter the complete signed number and select Celsius as the starting unit.
The Premeri temperature converter converts individual readings between Celsius, Fahrenheit and Kelvin. Select the source scale from the original thermometer, forecast or document; the number 25 by itself does not identify a temperature scale.
Use the offset as well as the scale factor
°F = °C × 9/5 + 32 °C = (°F − 32) × 5/9 K = °C + 273.15 °C = K − 273.15
For a reading of 25 °C, first multiply 25 by 9/5 to obtain 45, then add 32: the result is 77 °F. Adding 273.15 to the same Celsius reading gives 298.15 K. Kelvin uses K without a degree symbol.
| Celsius | Fahrenheit | Kelvin |
|---|---|---|
| −40 °C | −40 °F | 233.15 K |
| 0 °C | 32 °F | 273.15 K |
| 25 °C | 77 °F | 298.15 K |
| 100 °C | 212 °F | 373.15 K |
Do not add 32 to a temperature difference
Suppose a room warms from 20 °C to 25 °C. The change is 5 Celsius degrees. Converting the readings gives 68 °F and 77 °F, so the change is 9 Fahrenheit degrees. Entering 5 °C into a converter for individual readings instead gives 41 °F, which answers a different question.
Change in °F = change in °C × 9/5 Change in °C = change in °F × 5/9 5 °C of change = 9 °F of change = 5 K of change
For a temperature difference, the Celsius and Kelvin interval sizes are equal, and the offset is omitted. Premeri's temperature tool is a reading converter, not a separate temperature-difference mode. To check a change with it, convert both end readings and subtract the results, retaining enough digits.
Check the absolute-zero boundary
In the ordinary temperature scales used by this converter, 0 K corresponds to −273.15 °C and −459.67 °F. Premeri rejects readings below these limits rather than returning a negative Kelvin result. The boundary values themselves are accepted.
If a conversion is rejected, first check the selected scale and whether the source uses a decimal point or comma. Do not remove a minus sign merely to make the field accept a reading. This tool is intended for ordinary measurement conversions; it does not model specialized physical systems described using negative absolute temperatures.
Keep the source's precision and purpose in mind
If a forecast reports 25 °C rounded to a whole degree, a converted result of 77 °F does not establish the temperature more precisely than the original report. Likewise, an oven setting is a setpoint, not proof of the temperature at every location inside the oven. Convert the unit, then follow the requirements of the actual task.
The examples here are arithmetic checks, not instructions for medical treatment, food safety or equipment operation. For any such task, use the relevant professional or manufacturer guidance and the original measurement conditions.
Unit relationships
How the examples were prepared
These examples were prepared for Premeri and use fictional measurements. The calculations are shown so you can check each step. Report a specific error through our contact page.