Convert a temperature across eight historical scales at once — Celsius, Fahrenheit, Kelvin, Rankine, Réaumur, Newton, Delisle, and Rømer. Type into any field and the rest update instantly. Below absolute zero, fields shade as a warning because no real substance can be that cold.
| Reference | °C | °F | K | °R |
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Celsius (1742) is anchored to the freezing and boiling points of water at standard pressure — the everyday scale used almost everywhere except the United States. Fahrenheit (1724) put 0°F at a brine freezing point and 96°F near body temperature; later refinements pinned water freezing at 32°F and boiling at 212°F. Kelvin (1848) shares the Celsius degree size but starts at absolute zero — the SI unit for thermodynamic temperature. Rankine (1859) does the same for Fahrenheit: same degree size, but zero is absolute zero. Used in some U.S. engineering. Réaumur (1730) sets water freezing at 0 and boiling at 80; lingered in 19th-century cheese-making. Newton (~1700) is one of Isaac Newton's earliest attempts — 0 at freezing water, 33 at boiling. Delisle (1732) is inverted: 0 at boiling, 150 at freezing. Used in Russia for ~100 years. Rømer (1701) was the Danish predecessor that inspired Fahrenheit: 0 at brine, 60 at water boiling.