Rankine to Delisle
°R
°De
Conversion History
| Conversion | Reuse | Delete |
|---|---|---|
| No conversion history to show. | ||
Quick Reference Table (Rankine to Delisle)
| Rankine (°R) | Delisle (°De) |
|---|---|
| 0 | 559.725 |
| 459.67 | 176.66666666666666666667 |
| 491.67 | 150 |
| 527.67 | 120 |
| 558.27 | 94.5 |
| 671.67 | 0 |
About Rankine (°R)
Rankine (°R) is an absolute temperature scale that uses Fahrenheit-sized degrees. Like the kelvin it starts at absolute zero (0°R), but its degree intervals match Fahrenheit rather than Celsius. This makes it useful in US customary engineering thermodynamics — particularly older American aerospace, HVAC, and mechanical engineering literature — where Fahrenheit-based calculations must account for absolute temperature. Water freezes at 491.67°R, boils at 671.67°R, and body temperature is 558.27°R. The Rankine scale is rarely used today outside legacy US engineering calculations; SI units with kelvin have largely replaced it internationally and increasingly within the US engineering community as well.
Jet engine combustion temperatures around 2,500°F (1,371°C) equal approximately 2,960°R in thermodynamic calculations. Cryogenic oxygen (−183°C) is about 163°R.
Etymology: Named after Scottish engineer William John Macquorn Rankine (1820–1872), who proposed the scale in 1859. Rankine made major contributions to thermodynamics, steam engine theory, and civil engineering. The Rankine cycle — the theoretical model for steam power plants — is also named after him.
About Delisle (°De)
The Delisle scale (°De) is a historical temperature scale with an inverted direction: higher Delisle values mean colder temperatures. Created by French astronomer Joseph-Nicolas Delisle in 1732, it sets 0°De at the boiling point of water and counts upward as temperature falls; the freezing point is 150°De. This inversion arose because Delisle calibrated his mercury thermometer so that mercury contracted with cooling, measuring degrees of cooling from the boiling point rather than degrees of warmth above a cold reference. The scale was used extensively in Russia for most of the 18th century, notably by Mikhail Lomonosov, before being replaced by Celsius. Today it is an educational curiosity with no practical use.
Boiling water is 0°De; freezing is 150°De. A typical room at 20°C is 120°De. Absolute zero is approximately 559.73°De.
Etymology: Named after Joseph-Nicolas Delisle (1688–1768), a French astronomer who worked in St. Petersburg at the invitation of Peter the Great from 1726. He devised the scale in 1732 while in Russia, where it was adopted and remained in scientific use until the late 18th century when Celsius became standard.
Rankine – Frequently Asked Questions
What is the Rankine scale used for?
Rankine is used in US customary thermodynamic calculations where absolute temperature is needed but Fahrenheit-scale degrees are preferred. It appears in older American engineering standards for steam power, HVAC, and aerospace — disciplines where engineers needed an absolute scale compatible with Fahrenheit-unit formulas without converting to kelvin.
How does Rankine differ from kelvin?
Both start at absolute zero (0 K = 0°R), but their degree sizes differ. One kelvin equals 1.8 Rankine degrees, matching the 1.8 ratio between Celsius and Fahrenheit degree sizes. So 273.15 K = 491.67°R. To convert: °R = K × 1.8.
How do you convert Rankine to Celsius?
Divide by 1.8 to get kelvin, then subtract 273.15. Formula: °C = (°R / 1.8) − 273.15. For example, 491.67°R ÷ 1.8 = 273.15 K; 273.15 − 273.15 = 0°C. Alternatively: °C = (°R − 491.67) / 1.8.
What is absolute zero in Rankine?
Absolute zero is 0°R, the same as 0 K and −273.15°C (−459.67°F). Because Rankine starts at absolute zero, it has no negative values — a property shared with kelvin. This is what makes it useful in thermodynamics: equations requiring absolute temperature work directly without offset corrections.
Is Rankine still used in modern engineering?
Rankine use has declined significantly. Most modern engineering, including US aerospace and HVAC standards, has shifted to SI units (kelvin). Rankine persists mainly in legacy documents, some US university thermodynamics courses that teach both systems, and niche industries still working from older US customary standards. New engineering work rarely specifies Rankine.
Delisle – Frequently Asked Questions
Why is the Delisle scale inverted?
Delisle calibrated his thermometer by observing how mercury contracted as it cooled from boiling water. He measured degrees of cooling rather than degrees of warmth — the scale counted how far the temperature had dropped from the boiling point. This made 0°De the starting reference (boiling) and larger numbers represent lower temperatures, the opposite of every other common scale.
What is the freezing point of water on the Delisle scale?
The freezing point of water is 150°De. The boiling point is 0°De. The scale spans 150 degrees between freezing and boiling — contrast with 100 degrees in Celsius or 180 degrees in Fahrenheit. To convert: °De = (100 − °C) × 1.5, so 0°C gives (100 − 0) × 1.5 = 150°De.
Who invented the Delisle scale and where was it used?
Joseph-Nicolas Delisle invented the scale in St. Petersburg in 1732, where he had been invited to work by Peter the Great. The scale was adopted by Russian scientists and used throughout the 18th century, particularly by Mikhail Lomonosov. It was later standardized by Joseph-Nicolas's colleague Joseph-Adam Braun, who fixed the two reference points.
How do you convert Delisle to Celsius?
Subtract the Delisle value from 100, then multiply by 2/3. Formula: °C = 100 − (°De × 2/3). For example, 150°De → 100 − (150 × 2/3) = 100 − 100 = 0°C (freezing). For 0°De → 100 − 0 = 100°C (boiling). Remember the scale is inverted: higher Delisle = colder temperature.
What other temperature scales run backwards like Delisle?
Delisle is the only well-known inverted temperature scale, but the concept appears elsewhere. Astronomical magnitude runs backwards (brighter stars have lower numbers). The Scoville scale for chilli heat is not inverted but is logarithmically compressed in a way that confuses people similarly. In thermometry, Delisle stands alone — every other scale (Celsius, Fahrenheit, Kelvin, Rankine, Newton, Rømer, Réaumur) increases with heat. The inversion made Delisle unintuitive, which is a key reason it lost out to Celsius.