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Celsius to Delisle Converter
↔ Convert °De to °C instead

Common Conversions

°C °De
-273.15 559.73
-100 300
-40 210
0 150
20 120
25 112.5
37 94.5
50 75
75 37.5
100 0
150 -75
200 -150

Why this conversion matters in chemistry

Joseph-Nicolas Delisle proposed his thermometer scale in 1732 with two unusual choices: zero at the boiling point of water, and the scale running backwards so that colder temperatures give larger numbers. The freezing point lands at 150 °De. The scale stayed in use in Russian meteorology and chemistry through the nineteenth century before Celsius took over. The conversion comes up most as historical bookkeeping — translating an old chemistry record into modern Celsius — but it's a useful exercise in unit-conversion mechanics, since both the offset and the direction are nonstandard.

Formula

°De = (100 − °C) × 3/2

Worked Examples

0°C = 150°De

The freezing point of water — at the high end of the Delisle scale, which is upside-down compared to Celsius.

100°C = 0°De

The boiling point of water — Delisle's chosen zero, which is what makes the whole scale run backwards.

25°C = 112.5°De

Standard lab temperature, expressed in Delisle units — useful as a sanity check on the inverted-scale arithmetic.

-40°C = 210°De

An extremely cold temperature, the kind that comes up in cryogenic chemistry — and a good test of the scale's inverted direction.

Frequently Asked Questions

How do I convert Celsius to Delisle?
Subtract the Celsius value from 100, then multiply by 3/2. So 25 °C becomes (100 − 25) × 1.5 = 112.5 °De.
What is the Delisle scale?
A historical temperature scale proposed by Joseph-Nicolas Delisle in 1732. Zero sits at the boiling point of water, 150 sits at the freezing point — the scale runs backwards from most others, so higher numbers mean colder temperatures.
Why is the Delisle scale inverted?
Delisle designed his thermometer to measure cooling, so the original calibration counted upward as the temperature dropped. The convention stuck even after thermometry settled on the rising-scale designs that became Celsius and Fahrenheit.
Is the Delisle scale used in modern chemistry?
No — Celsius and Kelvin handle everything. Delisle survives only in eighteenth- and nineteenth-century historical references, particularly older Russian scientific literature, where converting back to Celsius is the first step before any modern comparison.