Temperature readings versus temperature changes
A reading is a position on a temperature scale. A difference is the size and direction of a change. The selected quantity type controls whether offsets such as 32 or 273.15 are applied. The table follows the same mode as the main result.
For a separate distance-unit conversion, use the Length Converter ; temperature offsets do not apply to its proportional length factors.
The formula
Celsius and Kelvin have equally sized intervals but different zero points. Fahrenheit intervals are smaller, so a change of one Celsius degree is a change of 1.8 Fahrenheit degrees. Converting a temperature difference uses scaling only, without a zero-point offset. Rankine has the same interval size as Fahrenheit and the absolute zero point of Kelvin. Its reading lower boundary is 0°R; signed changes use scaling without offsets.
A freezing-point reading and a warming interval
In Temperature reading mode, 0 °C converts to 32 °F and 273.15 K. In Temperature difference mode, a rise of 10 °C converts to a rise of 18 °F or 10 K. Adding 32 to that temperature change would be incorrect.
How to use this calculator
- Choose a temperature reading or difference/change.
- Enter the value and its source and target scales, including Rankine if needed.
- Read the live four-scale table; Reverse retains the same reading/change mode and Reset restores the example.
Choose reading or change before converting
A room reading of 20 °C and a room warming by 20 °C are different statements. The reading corresponds to 68 °F; the warming interval corresponds to 36 °F. The offset belongs to scale positions, not to differences between two positions.
Negative differences are allowed because they describe cooling. A change of −5 K is a drop of 5 °C, even though a physical absolute-temperature reading of −5 K is rejected by this tool.
Absolute zero sets a lower reading boundary
For ordinary thermodynamic temperature readings, the lower boundary is 0 K, equivalent to −273.15 °C or −459.67 °F. The converter rejects lower readings instead of displaying an impossible ordinary temperature.
Kelvin uses the symbol K without a degree sign. Celsius and Fahrenheit use °C and °F. Values displayed with extra decimal digits are numerical conversions, not a claim that the original thermometer was that precise.
Rankine readings and reverse conversion
A reading of 20 °C is 68 °F, 293.15 K or 527.67 °R. A change of 10 °C is 18 °F or 18 °R, and a change of −10 °R is allowed even though a reading of −10 °R is below absolute zero.
Reverse this conversion uses the target amount as the new source value and keeps the selected reading/change mode. It preserves the same quantity; it does not switch a reading into an interval.
Assumptions & limitations
What this calculation assumes
- The scales are Celsius, Fahrenheit, and Kelvin under their standard conversion relationships.
- Reading mode represents ordinary thermodynamic temperatures at or above absolute zero.
What to keep in mind
- Historical scales beyond Celsius, Fahrenheit, Kelvin and Rankine are not included.
- The calculator changes units; it does not model heat transfer, thermal expansion, or instrument calibration.
Common questions
Why does zero Celsius become 32 Fahrenheit?
The scales have different zero points. The reading formula applies both the interval scale factor and a 32-degree offset.
Can I enter a negative Kelvin change?
Yes, in Temperature difference mode. It represents a decrease. A negative Kelvin reading is rejected in Temperature reading mode.
Are a Celsius degree and a kelvin the same size?
Their intervals are equal. A change of one Celsius degree equals a change of one kelvin, while their reading zero points differ.
Is a Rankine degree the same size as a Fahrenheit degree?
Yes. Their intervals have the same size, but their reading zero points differ by 459.67 degrees. Zero Rankine is absolute zero.
Sources & further reading
Reviewed on