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

Common Conversions

°De °C
0 100
37.5 75
75 50
112.5 25
120 20
150 0
200 -33.33
210 -40
300 -100
400 -166.67
500 -233.33
559.73 -273.15

Why this conversion matters in chemistry

Pre-Celsius thermochemistry archives from 18th- and 19th-century Russian laboratories report temperatures in Delisle. The scale runs backwards: 0 °De marks water's boiling point, and the number increases as temperature drops, so a Delisle reading is a kind of inverted Celsius. A 100 °De entry corresponds to 33.3 °C — the conversion needed to drop a historical reaction enthalpy or solubility measurement onto the same axis as a modern calorimetric value. The factor 2/3 °C per °De is just the 1.5° step Delisle chose to span the same range Celsius covered with 1°.

Formula

°C = 100 − (°De × 2/3)

Worked Examples

0°De = 100°C

Water's boiling point — the calibration anchor at the Delisle zero.

150°De = 0°C

Water's freezing point on the Delisle scale — the upper anchor.

112.5°De = 25°C

Standard lab temperature in Delisle units — useful for benchmark comparison.

300°De = -100°C

Cryogenic regime — the kind of temperature low-temperature chemistry handles.

Frequently Asked Questions

How do I convert Delisle to Celsius?
Multiply the Delisle value by 2/3, then subtract from 100. For example, 150 °De gives 100 − (150 × 2/3) = 100 − 100 = 0 °C.
What is 0 °De in Celsius?
Exactly 100 °C — water's boiling point. The Delisle scale runs backwards: numbers grow as temperature drops, so the boiling point sits at the zero and the freezing point at 150.
Who invented the Delisle scale?
Joseph-Nicolas Delisle, a French astronomer, in 1732. It was the standard thermometric scale in Russia for about a century before Celsius and Réaumur replaced it. The scale survives only in historical archives.
Can Delisle values be negative?
Yes. Negative Delisle corresponds to temperatures above water's boiling point. For example, −75 °De equals 150 °C — the inverted scale runs into negatives once you cross above 100 °C.