About

Incorrect temperature conversion causes real failures: furnace miscalibration, pharmaceutical storage violations, laboratory reproducibility errors. This tool converts between all 6 historical and SI temperature scales using Kelvin (K) as the canonical intermediate. Every conversion passes through the thermodynamic absolute zero reference, eliminating cumulative rounding from chained formulas. Input in any scale produces simultaneous output in the remaining five.

The converter handles negative values, absolute zero clamping, and fractional precision to 6 significant figures. Note: the Delisle scale is inverted - higher values represent colder temperatures. Réaumur remains in use for some European cheese and sugar industries. This tool approximates ideal gas thermometry conditions and does not account for ITS-90 fixed-point interpolation below 13.8 K.

Formulas

All conversions route through Kelvin as the thermodynamic hub. For a source value T in any scale, the tool first computes K, then derives every other scale from K.

toKelvin:

K = T_°C + 273.15

K = T_°F − 321.8 + 273.15

K = T_K

K = T_°R1.8

K = T_°Ré × 1.25 + 273.15

K = 373.15 − T_°De × 23

fromKelvin:

T_°C = K − 273.15

T_°F = (K − 273.15) × 1.8 + 32

T_K = K

T_°R = K × 1.8

T_°Ré = (K − 273.15) × 0.8

T_°De = (373.15 − K) × 1.5

Where K = absolute temperature in Kelvin. Values below 0 K are physically meaningless and flagged with a warning. The constant 273.15 is the ice-point offset defined by the SI. The factor 1.8 (equivalently 95) converts between Celsius-sized and Fahrenheit-sized degrees.

Reference Data

Scale	Symbol	Absolute Zero	Water Freezes	Water Boils	Body Temp (Human)	Inventor	Year	Usage
Celsius	°C	−273.15	0	100	37	Anders Celsius	1742	Worldwide (SI-derived)
Fahrenheit	°F	−459.67	32	212	98.6	Daniel Fahrenheit	1724	USA, Cayman Islands, Liberia
Kelvin	K	0	273.15	373.15	310.15	Lord Kelvin	1848	SI base unit (science)
Rankine	°R	0	491.67	671.67	558.27	W. J. M. Rankine	1859	US engineering (thermodynamics)
Réaumur	°Ré	−218.52	0	80	29.6	R. A. F. de Réaumur	1730	Cheese & sugar production (EU)
Delisle	°De	559.725	150	0	94.5	Joseph-Nicolas Delisle	1732	Historical (Russia, 18th c.)
Common Reference Points
Liquid Nitrogen	-	-	−195.79 °C = 77.36 K		-	-	-	Cryogenics
Dry Ice (CO⊂2)	-	-	−78.5 °C = 194.65 K		-	-	-	Shipping, lab
Room Temperature	-	-	20 - 25 °C = 68 - 77 °F		-	-	-	HVAC standard
Oven Baking	-	-	180 °C = 356 °F		-	-	-	Cooking
Steel Melting	-	-	1370 - 1530 °C		-	-	-	Metallurgy
Sun Surface	-	-	5,505 °C = 5,778 K		-	-	-	Astrophysics
Cosmic Microwave Background	-	-	−270.42 °C = 2.725 K		-	-	-	Cosmology

Frequently Asked Questions

Routing through Kelvin reduces the conversion matrix from 30 unique formulas (6 scales × 5 targets) to 12 functions (6 toKelvin + 6 fromKelvin). This eliminates compound rounding errors and ensures thermodynamic consistency since Kelvin is the SI base unit for thermodynamic temperature, anchored at absolute zero (0 K = −273.15 °C).

The tool flags any input that resolves to a Kelvin value below 0 K. Negative Kelvin values violate the Third Law of Thermodynamics. The conversion still runs so you can see the mathematical result, but a warning indicates the temperature is physically unrealizable. This is useful for catching input errors in engineering worksheets.

Joseph-Nicolas Delisle originally defined his scale in 1732 with the boiling point of water as 0 °De and measured downward. As temperature decreases, the Delisle value increases. This means 150 °De = 0 °C (freezing point). The formula is T_°De = (100 − T_°C) × 1.5.

The converter outputs 6 significant figures using IEEE 754 double-precision floating point. For the Sun's surface at approximately 5,778 K, this gives sub-Kelvin accuracy. However, at cosmic scales (e.g., 10⁹ K in neutron star cores), the 273.15 offset becomes negligible and Celsius effectively equals Kelvin. Floating-point errors remain below 1 part in 10¹⁵.

Yes. The Réaumur scale persists in European dairy (cheese aging temperatures) and confectionery (sugar syrup stages). For example, the "soft ball" sugar stage is 95 - 97 °Ré (118.75 - 121.25 °C). Some Italian and French culinary references still cite Réaumur. The scale divides the water liquid range into 80 degrees instead of 100.

Both are absolute scales (zero at absolute zero), but they differ in degree size. One Kelvin step equals one Celsius degree. One Rankine step equals one Fahrenheit degree. Therefore T_°R = 1.8 × T_K. Rankine is used in US thermodynamic engineering (Brayton cycle, gas turbine calculations) where Fahrenheit units are standard.