Convert Triple Point of Water to Delisle
Convert triple points of water to degrees delisle instantly. °De = 559.725 − (TPW × 409.74) — use the live calculator, the exact formula, a reference-temperature table and worked examples. Also check the Delisle to Triple Point of Water converter for the reverse conversion.
Units explained
Triple Point of Water
The triple point of water is the unique state at which ice, liquid water, and water vapor coexist in equilibrium — exactly 273.16 K (0.01 °C). Treated as a converter unit, 1 triple point of water equals exactly 273.16 kelvins.
Adopted as thermometry's master fixed point because it is exactly reproducible in a sealed glass cell, unlike freezing and boiling points, which shift with atmospheric pressure and dissolved impurities.
Calibration laboratories and the International Temperature Scale of 1990 (ITS-90); from 1954 to 2019 the kelvin itself was defined as exactly 1/273.16 of this temperature.
Fixed at exactly 273.16 K by the 10th CGPM in 1954; it remained the kelvin's defining point until the 2019 SI redefinition through the Boltzmann constant.
Delisle
The degree Delisle (°De) is a famously reversed scale: water boils at 0 °De and freezes at 150 °De, so numbers increase as temperature falls. One degree Delisle corresponds to exactly −2/3 of a kelvin.
Invented by French astronomer Joseph-Nicolas Delisle while directing the observatory in St. Petersburg, Russia; his thermometers were originally graduated by the contraction of mercury cooling down from the boiling point of water.
Widely used in 18th-century Russia for about a century. Today it appears only in the history of thermometry, where it is the textbook example of an inverted temperature scale.
Created by Joseph-Nicolas Delisle in St. Petersburg in 1732; recalibrated to the familiar 150-division form by Josias Weitbrecht in 1738.
Triple Point of Water to Delisle conversion formula
The exact relationship between triple points of water and degrees delisle:
To convert triple points of water to degrees delisle, multiply the value by 409.74 and subtract the result from 559.725. To reverse, multiply the value by 0.00244057207 and subtract the result from 1.3660492019.
Reference anchors: water freezes at 0.9999633914 TPW = 150 °De and boils at 1.3660492019 TPW = 0 °De (at standard atmospheric pressure).
How to use this converter
Type a value into the calculator. The result in degrees delisle updates as you type. Tap a quick value, copy the result with one click, or use the swap arrow to jump straight to the Delisle to Triple Point of Water converter for the reverse direction.
Step-by-step: convert triple points of water to degrees delisle
- Write down the temperature in triple points of water (TPW).
- Multiply the value by 409.74 and subtract the result from 559.725.
- The result is the same temperature expressed in degrees delisle (°De).
- To reverse, multiply the value by 0.00244057207 and subtract the result from 1.3660492019 — or open the Delisle to Triple Point of Water converter.
Worked examples
Example 1 — Convert 1 TPW to °De:
559.725 − (1 × 409.74) = 149.985 °De
Example 2 — Convert 100 TPW to °De:
559.725 − (100 × 409.74) = -40414.275 °De
Triple Point of Water to Delisle conversion table
Physically meaningful reference temperatures, from absolute zero to the surface of the Sun, converted from triple points of water to degrees delisle:
| Triple Point of Water [TPW] | Delisle [°De] | Reference point |
|---|---|---|
| 0 | 559.725 | Absolute zero |
| 0.8535290672 | 210 | Where Celsius and Fahrenheit coincide (−40°) |
| 0.9348814695 | 176.6666666667 | Zero Fahrenheit (0 °F) |
| 0.9999633914 | 150 | Water freezes (0 °C / 32 °F) |
| 1 | 149.985 | Triple point of water |
| 1.0365719725 | 135 | Cool day (10 °C / 50 °F) |
| 1.0731805535 | 120 | Room temperature (20 °C / 68 °F) |
| 1.091484844 | 112.5 | Standard laboratory temperature (25 °C) |
| 1.1097891346 | 105 | Hot day (30 °C / 86 °F) |
| 1.1354151413 | 94.5 | Human body temperature (37 °C / 98.6 °F) |
| 1.1463977156 | 90 | Heat-wave day (40 °C / 104 °F) |
| 1.1830062967 | 75 | Hot tap water (50 °C / 122 °F) |
| 1.3660492019 | 0 | Water boils (100 °C / 212 °F) |
| 1.6589178503 | -120 | Moderate baking oven (180 °C / 356 °F) |
| 21.1524381315 | -8107.275 | Surface of the Sun (≈5,505 °C) |
Frequently asked questions
What is 1 TPW in °De?
How do I convert triple points of water to degrees delisle?
How do I convert degrees delisle back to triple points of water?
At what temperature do the Triple Point of Water and Delisle scales read the same number?
Can a temperature be below absolute zero?
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Sources & references
Conversion relationship (°De = 559.725 − (TPW × 409.74)) verified against the following authoritative sources:
- BIPM — The International System of Units (SI Brochure 9th ed.)
Official BIPM publication defining the seven SI base units (including the meter) and the rules for their use. The global authority on units of measurement.
- NIST — Guide to the SI
US National Institute of Standards and Technology reference covering the SI base and derived units with definitions and usage rules for US technical practice.
- NIST Special Publication 811 — Guide for the Use of the International System of Units
Detailed NIST guide covering exact conversion factors between SI and US customary units along with formatting and rounding conventions.
- BIPM — International Temperature Scale of 1990 (ITS-90)
The internationally agreed practical temperature scale, defining fixed points (including the triple point of water at 273.16 K) and interpolation instruments used by national metrology institutes for thermometer calibration worldwide.
- CODATA Internationally Recommended Values of the Fundamental Physical Constants
Committee on Data of the International Science Council; authoritative source for the masses of fundamental particles (electron, proton, neutron) and the atomic mass constant.