Result in Celsius
—
Equivalent temperature
Accurate temperature conversion between Réaumur (°Ré) and Celsius (°C) — the simplest temperature scale relationship
Convert Réaumur to Celsius instantly using the exact formula. Full multi-scale breakdown into Fahrenheit, Kelvin, and Rankine — all in one free tool for 2026.
Professional temperature conversion for historical research, culinary arts, scientific literature, and meteorology
Réaumur and Celsius share the same zero point (water freezes at 0°Ré and 0°C), making this the simplest of all temperature conversions — no offset is needed, only a multiplication. The Réaumur scale spans 80 degrees from freezing to boiling (0–80°Ré), while Celsius spans 100 degrees (0–100°C) for the same physical interval. The exact ratio is 5/4: °C = °Ré × 5/4 = °Ré × 1.25 and °Ré = °C × 4/5 = °C × 0.8. No more formula is needed — completely exact, no approximation.
Switch instantly between Réaumur → Celsius and Celsius → Réaumur conversion modes. The results panel simultaneously displays the equivalent temperature in all five major scales — Réaumur, Celsius, Fahrenheit, Kelvin, and Rankine — giving you complete cross-scale context from a single input. This is especially useful for researchers and food historians who encounter Réaumur values in old texts and need to cross-reference against modern Celsius, Fahrenheit, and Kelvin values from a single calculation.
Essential for historians and academics studying 18th–19th century European scientific literature — where Réaumur was the dominant scale in France, Germany, Russia, and the Netherlands for over 100 years. Food scientists and culinary historians interpreting vintage French, German, and Russian recipes that specify temperatures in Réaumur (e.g. caramel stages, candy making, bread proving). Meteorologists translating pre-1800s European weather records. Students studying the history of science and the development of temperature measurement standards.
Select conversion direction, enter your temperature value, and get instant multi-scale results
The Réaumur scale was invented in 1730 by French scientist René Antoine Ferchault de Réaumur, who calibrated his thermometer using a mixture of water and alcohol. He defined the freezing point of water as 0°Ré and the boiling point as 80°Ré — the same two reference points used by Anders Celsius in 1742, except Celsius stretched the interval to 100 degrees. This shared zero point makes the Réaumur-Celsius conversion uniquely elegant: since both scales start at 0°C = 0°Ré, only a multiplication factor is needed and no addition or subtraction offset is required.
The conversion factor comes directly from the ratio of the two scales' boiling-to-freezing intervals: Celsius has 100 degrees between the two reference points; Réaumur has 80. So 100°C = 80°Ré, which simplifies to 1°C = 0.8°Ré and 1°Ré = 1.25°C. The factor 5/4 (= 1.25) converts °Ré to °C, and 4/5 (= 0.8) converts °C to °Ré. This 5:4 ratio also means that Réaumur degrees are larger than Celsius degrees — each Réaumur degree spans 1.25°C, making it a more "coarse" scale than Celsius. The Réaumur scale was officially abandoned in most of Europe by the mid-19th century as Celsius became the international standard.
Example: 20°Ré × 1.25 = 25°C | 37°C × 0.8 = 29.6°Ré (body temp)
Shared zero: 0°Ré = 0°C | Factor: 1°Ré = 1.25°C | 1°C = 0.8°Ré | 80°Ré = 100°C = 212°F = 373.15 K
To convert Réaumur to Celsius, simply multiply the °Ré value by 1.25 (or 5/4). No offset is needed since both scales share the same zero point. Here are three worked examples:
Input: 20°Ré
Formula: °C = 20 × 1.25
= 25°C
= comfortable warm room / summer day
Input: 29.6°Ré
Formula: °C = 29.6 × 1.25
= 37°C
= normal human body temperature
Input: 160°Ré
Formula: °C = 160 × 1.25
= 200°C
= moderate baking oven (392°F / Gas Mark 6)
°Ré → °C: Multiply by 1.25 — or equivalently, multiply by 5 then divide by 4. Quickest mental method: add 25% to the °Ré value. Example: 40°Ré → 40 + 10 = 50°C. °C → °Ré: Multiply by 0.8 — or equivalently, multiply by 4 then divide by 5. Quickest: subtract 20% from the °C value. Example: 25°C → 25 − 5 = 20°Ré. Key benchmarks: 0°Ré = 0°C, 10°Ré = 12.5°C, 20°Ré = 25°C, 40°Ré = 50°C, 80°Ré = 100°C. Since both scales share zero, negative values work identically: −10°Ré = −12.5°C, −40°Ré = −50°C.
Complete reference table covering sub-zero temperatures through high oven temperatures, with Celsius, Fahrenheit, and Kelvin equivalents and real-world context. Desktop shows the full table; mobile shows grouped cards below.
| Réaumur (°Ré) | Celsius (°C) | Fahrenheit (°F) | Kelvin (K) | Real-World Reference |
|---|---|---|---|---|
| −40°Ré | −50°C | −58°F | 223.15 K | Extreme Arctic cold |
| −32°Ré | −40°C | −40°F | 233.15 K | Celsius = Fahrenheit crossover |
| −20°Ré | −25°C | −13°F | 248.15 K | Deep winter freeze |
| −16°Ré | −20°C | −4°F | 253.15 K | Severe frost |
| −10°Ré | −12.5°C | 9.5°F | 260.65 K | Heavy frost / frozen ground |
| −8°Ré | −10°C | 14°F | 263.15 K | Winter cold |
| 0°Ré | 0°C | 32°F | 273.15 K | Water freezing point |
| 4°Ré | 5°C | 41°F | 278.15 K | Cold spring morning |
| 8°Ré | 10°C | 50°F | 283.15 K | Cool weather |
| 12°Ré | 15°C | 59°F | 288.15 K | Mild spring day |
| 16°Ré | 20°C | 68°F | 293.15 K | Comfortable room temperature |
| 20°Ré | 25°C | 77°F | 298.15 K | Warm room / summer day |
| 24°Ré | 30°C | 86°F | 303.15 K | Hot summer day |
| 28°Ré | 35°C | 95°F | 308.15 K | Very hot / heat wave |
| 29.6°Ré | 37°C | 98.6°F | 310.15 K | Normal body temperature |
| 32°Ré | 40°C | 104°F | 313.15 K | High fever |
| 36°Ré | 45°C | 113°F | 318.15 K | Very hot water (tap maximum) |
| 40°Ré | 50°C | 122°F | 323.15 K | Scalding water |
| 48°Ré | 60°C | 140°F | 333.15 K | Pasteurisation temperature |
| 60°Ré | 75°C | 167°F | 348.15 K | Near-boiling / hot beverage |
| 80°Ré | 100°C | 212°F | 373.15 K | Water boiling point (sea level) |
| 100°Ré | 125°C | 257°F | 398.15 K | Pressure cooking |
| 120°Ré | 150°C | 302°F | 423.15 K | Low oven (baking cakes) |
| 140°Ré | 175°C | 347°F | 448.15 K | Moderate oven |
| 160°Ré | 200°C | 392°F | 473.15 K | Standard baking temperature |
| 180°Ré | 225°C | 437°F | 498.15 K | Hot oven (roasting) |
| 200°Ré | 250°C | 482°F | 523.15 K | Very hot oven |
| 240°Ré | 300°C | 572°F | 573.15 K | Pizza oven / self-cleaning oven |
🔵 Blue row = water freezing | 🟧 Orange rows = body/room temperature | 🔴 Red row = water boiling
René Antoine Ferchault de Réaumur (1683–1757) was a French scientist best known for his studies of insects and iron-making, but his thermometer design became one of the most widely used in Europe for over a century. His scale used a dilute alcohol-water solution (rather than pure mercury) whose expansion coefficient he measured carefully. He set 0°Ré at the freezing point of water and defined the boiling point of his specific mixture — which happened to correspond to 80 divisions on his stem — as his upper reference. When compared to water's boiling point, this maps to 80°Ré = 100°C exactly.
The Réaumur scale was the dominant temperature scale in France, Germany, Russia, the Netherlands, and Scandinavia throughout the 18th and early 19th centuries. Scientific papers, cookbooks, medical texts, and meteorological records from this period in these countries almost universally use Réaumur. Carl Linnaeus, the famous Swedish botanist and taxonomist, used Réaumur temperatures in his botanical observations. Russian meteorological records from the 18th and early 19th centuries are recorded in Réaumur, requiring conversion for modern climate analysis.
Réaumur temperatures appear extensively in historic European cookbooks and confectionery guides, particularly for sugar work and candy making. The "thread stage" of sugar (about 107°C = 85.6°Ré), "soft ball" (116°C = 92.8°Ré), "hard crack" (149–154°C = 119.2–123.2°Ré), and caramel (160–180°C = 128–144°Ré) are all described in Réaumur in pre-1850s French and German patisserie texts. Food historians and professional chefs researching historical recipes regularly need this conversion.
The Celsius scale (originally called "centigrade") was proposed by Anders Celsius in 1742 and adopted by the scientific community rapidly due to its convenient 100-degree span. France officially adopted Celsius as part of the metric system following the French Revolution. Germany retained Réaumur longer — it was still used in some German scientific publications into the 1870s, and in everyday speech in some regions into the early 20th century. The last major holdout was Russia, which used Réaumur officially until the Soviet Union adopted the metric system in 1924.
Historians, archivists, and climate scientists working with pre-19th-century European documents regularly encounter Réaumur temperatures. Agricultural records, medical diaries, weather journals, and natural philosophy manuscripts from 1730–1850 in France, Germany, Russia, and the Netherlands predominantly use Réaumur. For example, Napoleon's famous Russian campaign of 1812 — where extreme cold played a decisive role — was recorded in Réaumur: temperatures of −20°Ré (= −25°C = −13°F) are mentioned in period accounts, and conversion to modern scales requires the ×1.25 formula.
Landmark scientific works that use Réaumur temperatures include the original botanical and zoological observations of Linnaeus, Réaumur's own 6-volume "Mémoires pour servir à l'histoire des insectes" (1734–1742), early European meteorological station records, and the chemical experiments of Lavoisier's contemporaries. Any researcher accessing primary sources in 18th-century European natural philosophy will need to convert Réaumur temperatures to modern equivalents to make sense of described experimental conditions and natural phenomena.
In 2026, the Réaumur scale has virtually no practical use in everyday life or modern science. It survives mainly as a historical curiosity and in the context of academic research into early modern science. However, it remains relevant for: (1) translating historical European scientific and culinary texts, (2) climate history research using 18th-19th century European meteorological records, (3) history of science education covering the development of temperature measurement, and (4) cheese-making in some traditional Swiss and Italian Alpine dairies, where historical Réaumur temperature references still appear in very old regional recipe manuscripts.
0°Ré = 0°C (shared zero — water freezing). 10°Ré = 12.5°C. 16°Ré = 20°C (room temperature). 20°Ré = 25°C (warm room). 29.6°Ré = 37°C (body temperature). 40°Ré = 50°C. 80°Ré = 100°C (water boiling). 160°Ré = 200°C (oven). Formula always: multiply °Ré by 1.25 for °C; multiply °C by 0.8 for °Ré. Unlike all other temperature conversions, no offset (addition/subtraction) is ever needed — only multiplication, making it the cleanest pairwise conversion in all of temperature metrology. Both negative and positive values use exactly the same formula.
A common mistake when working with Réaumur values is assuming the numbers are comparable to Celsius without conversion. A temperature of 40°Ré is NOT the same as 40°C — 40°Ré = 50°C (a scalding temperature), while 40°C is a high fever. Similarly, 80°Ré is boiling water, not a hot summer day. The Réaumur degree is 25% larger than a Celsius degree (1°Ré = 1.25°C), so Réaumur values are always smaller in number than their Celsius equivalents for positive temperatures. Always apply the ×1.25 factor before comparing or using a Réaumur temperature in any modern context — treating °Ré as °C without conversion will underestimate the actual temperature by 20%.
The Réaumur scale is a fascinating chapter in the history of measurement. René Antoine Ferchault de Réaumur published his thermometer design in 1730 in the Mémoires de l'Académie Royale des Sciences. The scale dominated European science and medicine for over a century alongside, and eventually displaced by, the Celsius scale introduced by Anders Celsius in 1742. Understanding these historical scales is essential for accurately interpreting primary sources from the 18th and early 19th centuries.
Read More →The National Institute of Standards and Technology provides authoritative definitions and exact conversion factors for all major temperature scales. NIST Special Publication 811 establishes the internationally accepted conversion factors between Réaumur, Celsius, Fahrenheit, Kelvin, and Rankine — confirming the exact 5/4 ratio used in this converter. NIST is the primary reference for metrological accuracy in all unit conversions.
Visit NIST →Explore the full library of free unit converters on ConceteMetric.com — covering temperature, pressure, length, weight, area, volume, and energy. All tools are mobile-friendly, scientifically accurate, and completely free to use throughout 2026 with no sign-up required. New converters are regularly added to the library.
All Converters →