HesapHanem

Delisle to Celsius Converter

Enter a temperature and choose a direction to convert between Delisle and Celsius.

How it is calculated

The conversion is a straight line with a negative slope: °C = 100 − °De × 2/3 for Delisle to Celsius, and °De = (100 − °C) × 3/2 for the other way. °De is the Delisle reading and °C the Celsius reading, both as plain numbers. The factor 2/3 appears because one Delisle degree is two thirds the size of a Celsius degree, and the 100 is where the two scales cross over, since the Delisle zero sits at the boiling point of water. The result is rounded to two decimals for display, and the calculator also prints the reverse conversion of its own answer so you can check the round trip. Negative inputs are accepted, and the tool does not stop you from entering a value below absolute zero.

Worked example

Convert 90 °De to Celsius. First multiply by 2/3: 90 × 2/3 = 60. Then subtract that from 100: 100 − 60 = 40. The result is 40.00 °C. Converting back as a check, (100 − 40) × 3/2 = 90.00 °De, which matches the starting value. For the opposite direction, 37 °C gives (100 − 37) × 3/2 = 94.50 °De, which shows how a warm body temperature lands on a high Delisle number.

Try this example →

Common mistakes

  • Expecting the Delisle number to rise with temperature. The scale runs backwards, so a larger °De value means a colder temperature.
  • Leaving the direction on Delisle to Celsius when the number you typed is already in Celsius, which gives a wildly wrong answer instead of an error.
  • Applying the usual 9/5 or 1.8 factor from Fahrenheit conversions. Delisle uses 2/3 (or 3/2 in reverse), not 1.8.
  • Forgetting the offset of 100 and only multiplying by 2/3, which treats Delisle zero as if it were Celsius zero.
  • Trusting results below -273.15 °C. The calculator will happily convert a Delisle value above about 559.7 even though that temperature cannot exist.

About this calculator

The Delisle scale was devised in 1732 by French astronomer Joseph-Nicolas Delisle and, unusually, runs backwards from the scales we use today: it sets 0°De at the boiling point of water and 150°De at its freezing point, so a Delisle reading falls as temperature rises. It was used for weather observation in Russia for roughly a century after Delisle brought it to the St. Petersburg Academy of Sciences, before being displaced by Celsius.

Because Delisle degrees run in the opposite direction and use a different span (150° instead of Celsius's 100° between the same two reference points), the conversion is inverted: C = 100 − D × (2/3), and D = (100 − C) × 1.5. This calculator converts between the two scales in either direction.

Was this helpful?

You can pick up to 3 reactions.

Comments (1)

  • Editorial team

    Two anchor points let you test any Delisle reading in your head. Zero degrees Delisle must come out as 100.00 °C, and 150 must come out as 0.00 °C. Because the scale runs backwards, a higher Delisle number means a colder day, which surprises people reading old logbooks. Going the other way, 20 °C becomes 120.00 °De. Do you come across Delisle figures in old astronomy or weather records?

Popular calculators

Loan Calculator

Monthly payment, total interest and full amortization schedule.

Percentage Calculator

Percent change, percent of, and ratio calculations.

Discount Calculator

Calculate final price, savings, and discount amount.

BMI Calculator

Body mass index from height and weight (metric or imperial).

Age Calculator

Compute your exact age in years, months and days from a birth date.

Compound Interest Calculator

Calculate the final amount and interest earned with compounding.

All Calculators