Temperature Interval Converter
Convert a temperature <strong>difference</strong> (a rise, a drop or a range) between kelvin, degree Celsius, degree Fahrenheit, degree Rankine and degree Réaumur. Because an interval has no starting point, no offset is added: 10 °C of warming is 18 °F of warming.
Select two units to see the conversion factor.
This tool converts temperature differences only. For a thermometer reading such as 20 °C to °F, use the temperature converters, because a reading needs an offset that an interval does not.
Temperature Interval Formula
A temperature interval is converted by a pure ratio. One kelvin and one degree Celsius are the same size, one degree Fahrenheit and one degree Rankine are the same size and equal 5/9 K, and one degree Réaumur equals 1.25 K. Result = value × (source size in K ÷ target size in K). Negative values are allowed, because a temperature can fall as well as rise.
Temperature Interval vs Temperature Reading
A temperature reading says how hot something is on a scale with a fixed zero, so converting it needs an offset: 0 °C is 32 °F. A temperature interval (also called a temperature difference or ΔT) says how far apart two temperatures are. It has no zero point to shift, so converting it needs only a multiplier. Warming a room from 18 °C to 28 °C is a rise of 10 °C, which is 18 °F, not 50 °F.
The reason is the size of the degree. Between water freezing and boiling there are 100 Celsius degrees, 180 Fahrenheit degrees and 80 Réaumur degrees. One kelvin equals one Celsius degree, and one Rankine degree equals one Fahrenheit degree, so kelvin and Rankine are the absolute scales built on those two sizes.
Intervals are what appear in specific heat, thermal conductivity, heat transfer coefficients and thermal expansion, as in J/(kg·K) or W/(m²·°C). The “per degree” in those units is an interval, which is why those converters never use offsets.
Supported Units
This converter supports the following 6 interval units. “°C (centigrade)” is the older name for the same degree as Celsius. The last column gives the size of one degree in kelvin.
| Unit | Symbol | Value in K |
|---|---|---|
| Kelvin | K | 1 |
| Degree Celsius | °C | 1 |
| Degree centigrade | °C (centigrade) | 1 |
| Degree Fahrenheit | °F | 0.5555555556 |
| Degree Rankine | °R | 0.5555555556 |
| Degree Réaumur | °Ré | 1.25 |
How to Use the Temperature Interval Converter
- Type the temperature interval in the value box. Decimals and scientific notation such as 0.0025 or 2.5e-3 are accepted.
- Choose the From unit and the To unit.
- The result appears instantly, or press Convert Now. Very large or very small results are shown in scientific notation.
- Use Swap Units to reverse the conversion, Copy Result to copy the answer, open Show this value in all units for a full list, and Clear to start again.
Step-by-step by hand
- Find the size of each unit in the common base unit (K): 1 °C = 1 K and 1 °F = 0.5555555556 K.
- Divide the source size by the target size to get the conversion factor: 1 ÷ 0.5555555556 = 1.8, so 1 °C = 1.8 °F.
- Multiply by your value: 25 °C × 1.8 = 45 °F.
Negative values are accepted here, since a temperature can drop. Do not use this tool for thermometer readings: 25 °C is 77 °F as a reading, but a 25 °C difference is 45 °F.
Common Temperature Interval Conversions
- Celsius to Fahrenheit: a 25 °C rise equals 45 °F.
- Fahrenheit to Celsius: a 36 °F drop equals 20 °C.
- Kelvin to Rankine: 100 K equals 180 °R.
- Réaumur: 80 °Ré equals 100 °C.
- Freezing to boiling of water: 100 °C equals 180 °F and 80 °Ré.
- Cooling: a fall of 12 °F equals -6.666666667 °C.
Celsius Interval to Other Units
Quick reference for frequently used values
| Δ°C | Δ°F | Δ°R | Δ°Ré |
|---|---|---|---|
| 1 | 1.8 | 1.8 | 0.8 |
| 5 | 9 | 9 | 4 |
| 10 | 18 | 18 | 8 |
| 20 | 36 | 36 | 16 |
| 50 | 90 | 90 | 40 |
| 100 | 180 | 180 | 80 |
Where and Why This Conversion Is Used
- Heating and cooling design: the allowed temperature rise across a coil or exchanger.
- Weather and climate: temperature range and anomaly data.
- Engineering calculations: ΔT in heat transfer formulas must use the same degree as the coefficient.
- Cooking and laboratory work: how much a mixture warms or cools.
- Reading older sources: Rankine and Réaumur differences.
Limitations
- This tool never adds or subtracts 32 or 273.15. It must not be used to convert an actual temperature.
- If a problem gives two readings, first subtract them in one scale to get the interval, then convert the interval here.
Important Differences Between Related Heat Quantities
- Specific heat capacity, J/(kg·K): energy needed to warm one kilogram of a material by one kelvin. It is not the total heat capacity of an object (J/K), which also depends on how much material there is, and it is not molar heat capacity (J/(mol·K)).
- Heat density, J/m²: heat or radiant energy delivered per unit area over a period. Heat flux density, W/m² is the rate of that transfer, energy per area per time. They are not interchangeable.
- Heat flux density, W/m² is heat flow per area. The heat transfer coefficient, W/(m²·K) is heat flux per kelvin of temperature difference, so heat flux = coefficient × temperature difference.
- Thermal conductivity, W/(m·K) is a material property. The heat transfer coefficient is a property of a surface or an assembly, and thermal resistance, K/W belongs to one specific object. Resistance is not conductivity or resistivity: R = L ÷ (k × A) for a slab.
- Temperature interval vs temperature: a difference of 10 °C is a difference of 18 °F. A reading of 10 °C is 50 °F. Every unit here that contains “per degree” or “K” uses intervals, so no offset is ever applied.
Each converter changes units within one quantity only. Related tools: Temperature Interval, Thermal Expansion, Thermal Resistance, Thermal Conductivity, Specific Heat Capacity, Heat Density, Heat Flux Density, Heat Transfer Coefficient, Fuel Efficiency - Mass and Fuel Efficiency - Volume.