Temperature Unit Converter
| Unit | Symbol | Formula |
|---|---|---|
| Celsius | °C | — |
| Fahrenheit | °F | °C × 9/5 + 32 |
| Kelvin | K | °C + 273.15 |
| Rankine | °R | (°C + 273.15) × 9/5 |
| Delisle | °De | °C = 100 − °De × 2/3 |
| Rømer | °Rø | °C = (°Rø − 7.5) × 40/21 |
| Newton | °N | °C = °N × 100/33 |
How to Use
Overview
Temperature scales mix linear offsets such as Celsius, Fahrenheit and Kelvin with reversed scales such as Delisle, where water boils at zero and freezes at 150 so a larger number means colder, plus the historic Romer and Newton scales. This tool gives each scale its own affine branch instead of one shared slope: 100 C becomes 212 F, 0 C becomes 273.15 K, and -40 C coincides with -40 F, while Delisle and Rankine follow their own definitions. Rankine and Kelvin share the same zero, so only the size of a degree differs between them. Zero is shared between the absolute scales; the degree size is not. The historic scales are worth keeping because they still appear in old instruments and translated papers. Delisle was built for a thermometer where the liquid fell as it warmed, so its numbers run the opposite way from every modern scale and a careless linear conversion flips the sign of the result. Romer and Newton survive in Danish and early English texts, and both were defined before the fixed points of water were standardised, which is why their degree sizes differ from Celsius by simple fractions rather than decimals. Absolute zero is unreachable in practice, so the lowest entries in the table exist to show the offset rather than to describe a measured state; below that line the arithmetic still runs but the number no longer means anything physical. The fixed points themselves were revised over time, which is why a modern Celsius degree is pegged to absolute zero rather than to an ice bath measured in a particular laboratory.
Features
- Seven scales in one view: Celsius, Fahrenheit, Kelvin, Rankine, Delisle, Romer, Newton
- Linear scales convert affinely, keeping the defined 273.15 and 459.67 offsets
- The reversed scale is handled separately: 0 Delisle is boiling, 150 Delisle is freezing
- Historic Romer (7.5 for freezing) and Newton (0 to 33) use their original definitions
- Expression input and batch conversion with zero to eight decimals
- A reference table on the page lists the formula behind each scale for cross-checking
How to use
- Enter a temperature or expression, for example 36.5 or 98.6
- Pick the source scale: Celsius at home, Fahrenheit for English recipes, Kelvin for thermodynamics
- Leave the target empty for all seven results, or pin one such as Fahrenheit
- Check the -40 point, where Celsius and Fahrenheit agree, as a quick sanity test
- Paste several temperatures and export CSV for lab notes or an equipment list
Notes
- Seven scales are covered: Celsius, Fahrenheit, Kelvin, Rankine, Delisle, Romer and Newton, with Celsius as the base and every conversion an affine shift rather than a plain ratio.
- Celsius and Fahrenheit differ by a zero offset, so 0 C maps to 32 F and 100 C to 212 F; the two fixed points must never be turned into a scale factor.
- Delisle and Romer run backwards, with 0 De at the boiling point and 150 De at freezing, while one Romer degree is 40/21 C, so a rising value means falling temperature there.
- Absolute zero is -273.15 C, 0 K and 0 R; Kelvin takes no degree sign and is written 273.15 K rather than 273.15 K with a degree mark.
- Inputs below absolute zero still compute but carry no physical meaning; CSV exports numbers, so unify scales before batch work.
- -40 is the only point where Celsius and Fahrenheit agree, which makes it a fast check on any converter
- This tool converts scales only and does not compute heat, power or thermocouple corrections
- Decimals affect display only; round trips stay in double precision