Result in Fahrenheit
0°F
Equivalent temperature
Accurate temperature conversion between Réaumur (°Ré) and Fahrenheit (°F)
Convert Réaumur to Fahrenheit instantly using the exact formula. Full multi-scale breakdown into Celsius, Kelvin, and Rankine — all in one free tool for 2026.
Professional temperature conversion for scientific research, historical studies, culinary arts, and meteorology
The Réaumur scale (°Ré) was defined with water freezing at 0°Ré and boiling at 80°Ré, while the Fahrenheit scale places these at 32°F and 212°F. The exact conversion formula is °F = (°Ré × 9/4) + 32, derived from the ratio of the two scales' ranges: 180°F spans equal to 80°Ré, giving a factor of 180/80 = 9/4 = 2.25. This is a mathematically exact relationship — no approximation is involved.
Switch instantly between Réaumur → Fahrenheit and Fahrenheit → Réaumur conversion modes. The results panel simultaneously displays the equivalent temperature in all five major scales — Réaumur, Fahrenheit, Celsius, Kelvin, and Rankine — giving you complete cross-scale context from a single input without needing multiple separate tools or manual calculations across several formulas.
Essential for historians studying 18th–19th century European scientific literature (where Réaumur was dominant), food scientists interpreting vintage French and German culinary recipes that specify temperatures in Réaumur, researchers translating historical meteorological records, students studying the history of temperature measurement, and anyone working with primary source documents from pre-metric European science and medicine.
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The Réaumur temperature scale was invented by French scientist René Antoine Ferchault de Réaumur in 1730. It was the dominant temperature scale in continental Europe — especially France, Germany, and Russia — for over a century before being displaced by Celsius. The scale is defined with the freezing point of water at 0°Ré and the boiling point of water at 80°Ré. The Fahrenheit scale, created by Daniel Gabriel Fahrenheit in 1724, places these reference points at 32°F and 212°F respectively, giving a range of 180°F for the same 80°Ré interval.
From these two reference points, the conversion factor is derived directly: the ratio of the two scales' water-freezing-to-boiling ranges is 180°F ÷ 80°Ré = 9/4 = 2.25. So each degree Réaumur equals 2.25 degrees Fahrenheit in scale size. To convert °Ré to °F, multiply by 9/4 and then add the Fahrenheit offset (32°F) to account for the different zero points. To go the other way, subtract 32 from °F and multiply by 4/9. Both conversions are mathematically exact.
Example: 20°Ré × 2.25 + 32 = 77°F | 100°F: (100 − 32) × 4/9 = 30.22°Ré
Scale ratio: 180°F = 80°Ré | 1°Ré = 2.25°F | 1°F = 0.4444°Ré | Body temp: 29.6°Ré = 98.6°F
To convert Réaumur to Fahrenheit, multiply the °Ré value by 2.25 (or 9/4), then add 32. Here are three worked examples from common reference temperatures:
Input: 20°Ré
Formula: °F = (20 × 2.25) + 32
= 45 + 32 = 77°F
= comfortable room temperature (25°C)
Input: 29.6°Ré
Formula: °F = (29.6 × 2.25) + 32
= 66.6 + 32 = 98.6°F
= normal human body temperature (37°C)
Input: 160°Ré
Formula: °F = (160 × 2.25) + 32
= 360 + 32 = 392°F
= moderate baking oven (200°C)
The easiest shortcut: multiply °Ré by 2, then add 10%, then add 32. Example: 20°Ré → 40 + 4 + 32 = 76°F (exact is 77°F — within 1%). For a rough check: every 4°Ré ≈ 9°F, same as every 5°C ≈ 9°F but scaled differently. Key benchmarks to remember: 0°Ré = 32°F, 20°Ré = 77°F, 40°Ré = 122°F, 80°Ré = 212°F. Since °Ré and °C share a simple 5/4 ratio, convert °Ré → °C first (×1.25), then °C → °F (×1.8 + 32) if you find that easier.
Use this reference table to look up common Réaumur to Fahrenheit conversions at a glance, with Celsius and Kelvin equivalents and real-world context. Desktop shows the full table; mobile shows grouped cards below.
| Réaumur (°Ré) | Fahrenheit (°F) | Celsius (°C) | Kelvin (K) | Real-World Reference |
|---|---|---|---|---|
| −40°Ré | −40°F | −50°C | 223.15 K | Extreme arctic cold |
| −20°Ré | −13°F | −25°C | 248.15 K | Deep winter freeze |
| −10°Ré | 13.5°F (13.4) | −12.5°C | 260.65 K | Heavy frost |
| 0°Ré | 32°F | 0°C | 273.15 K | Water freezing point |
| 4°Ré | 41°F | 5°C | 278.15 K | Cold spring morning |
| 8°Ré | 50°F | 10°C | 283.15 K | Cool weather |
| 12°Ré | 59°F | 15°C | 288.15 K | Mild spring day |
| 16°Ré | 68°F | 20°C | 293.15 K | Comfortable indoors |
| 20°Ré | 77°F | 25°C | 298.15 K | Warm room / summer day |
| 24°Ré | 86°F | 30°C | 303.15 K | Hot summer day |
| 28°Ré | 95°F | 35°C | 308.15 K | Very hot day / heat wave |
| 29.6°Ré | 98.6°F | 37°C | 310.15 K | Human body temperature |
| 32°Ré | 104°F | 40°C | 313.15 K | High fever |
| 40°Ré | 122°F | 50°C | 323.15 K | Scalding water |
| 60°Ré | 167°F | 75°C | 348.15 K | Near-boiling water |
| 80°Ré | 212°F | 100°C | 373.15 K | Water boiling point |
| 100°Ré | 257°F | 125°C | 398.15 K | Pressure cooking |
| 120°Ré | 302°F | 150°C | 423.15 K | Low oven (baking) |
| 160°Ré | 392°F | 200°C | 473.15 K | Moderate oven |
| 200°Ré | 482°F | 250°C | 523.15 K | Hot oven |
| 240°Ré | 572°F | 300°C | 573.15 K | Very hot oven / pizza oven |
🔵 Blue row = water freezing | 🟧 Orange rows = body/room temperature | 🔴 Red row = water boiling
The Réaumur scale was introduced by René Antoine Ferchault de Réaumur in 1730, predating both the Celsius scale (1742) and the later standardisation of Fahrenheit. Réaumur calibrated his thermometer using a water-alcohol mixture, setting the freezing point at 0° and the boiling point of the mixture at 80° — which he believed corresponded to pure water's boiling point. The 80-degree span was chosen because the alcohol solution expanded from 1,000 to 1,080 units in volume between the two fixed points, making 80 a naturally derived figure.
The Réaumur scale became extremely popular across 18th and 19th-century Europe. It was the primary temperature scale used in France, Germany, Switzerland, and Russia for scientific, medical, and meteorological work. Leo Tolstoy's novels frequently reference temperatures in Réaumur, and many historical European recipes — particularly French confectionery and German baking recipes — specify Réaumur temperatures for sugar work and oven settings. The scale was gradually superseded by Celsius for scientific use and by Fahrenheit in culinary contexts, and today it is considered obsolete for practical purposes but remains essential for historical interpretation.
Throughout the 18th and early 19th centuries, Réaumur was the standard temperature scale in European scientific publications. Works by Lavoisier, Euler, and Gauss occasionally reference temperatures in Réaumur. When translating or interpreting early scientific papers, meteorological diaries, medical case notes, or natural history observations from this period, converting Réaumur values to modern Fahrenheit or Celsius is essential for understanding the temperatures described.
Historical French and German cookbooks — particularly 18th and 19th-century confectionery and pastry works — routinely specify temperatures in Réaumur. Classic sugar-work stages (soft ball, hard crack, caramel) were described in Réaumur in many vintage recipe collections. A recipe calling for sugar heated to 120°Ré means 302°F (150°C) — a critical distinction for any culinary historian or chef attempting to recreate period-accurate recipes from primary sources.
Russia retained the Réaumur scale longer than most European countries, using it well into the 20th century for meteorology and daily life. Russian literature is full of Réaumur temperature references — Chekhov, Dostoevsky, and Tolstoy all used it naturally. A winter scene described as "−20 degrees" in a 19th-century Russian text almost certainly means −20°Ré (−13°F / −25°C), not Celsius. Historians, translators, and literary scholars working with Russian texts regularly need this conversion.
The Réaumur scale is studied in the history of science and measurement as an important milestone in the development of thermometry. Understanding how Réaumur's fixed-point approach (using phase changes of water as calibration points) influenced later scales — particularly Celsius and eventually the absolute Kelvin scale — is valuable for students of physics, chemistry, and the philosophy of measurement. The Réaumur-to-Fahrenheit relationship also provides an excellent worked example of linear scale conversion in mathematics education.
Centuries of European and Russian meteorological records were kept in Réaumur. Weather station logs, almanacs, agricultural records, and climate diaries from the 18th and 19th centuries across France, Germany, Austria, Switzerland, and Russia documented daily temperatures in Réaumur. Climate scientists and historical climatologists studying pre-industrial temperature trends must convert these archival readings to modern scales to incorporate them into long-term climate reconstructions and analyses.
Historical European pharmacopoeias, medical textbooks, and laboratory manuals from the 18th and 19th centuries specified reaction temperatures, storage conditions, and body temperature thresholds in Réaumur. Normal human body temperature was documented as approximately 29.6°Ré (= 98.6°F = 37°C) in period medical literature. Researchers studying the history of medicine, pharmacy, or physiology frequently encounter Réaumur values that must be converted to understand historical clinical contexts accurately.
0°Ré = 32°F = 0°C = 273.15 K (water freezes). 80°Ré = 212°F = 100°C = 373.15 K (water boils). 20°Ré = 77°F = 25°C (warm room). 29.6°Ré = 98.6°F = 37°C (body temperature). −14.22°Ré = 0°F = −17.78°C (Fahrenheit zero). Scale factor: 1°Ré = 2.25°F = 1.25°C. Negative Réaumur temperatures are below freezing (below 0°Ré). Because the Réaumur degree is 2.25 times larger than a Fahrenheit degree, differences in Réaumur appear smaller than the equivalent Fahrenheit differences.
The most common error when working with historical European temperatures is confusing Réaumur with Celsius. Both scales set water's freezing point at 0° — but Réaumur's boiling point is 80° while Celsius is 100°. So a historical record of "80 degrees" in a European text almost certainly means 80°Ré = 212°F = 100°C (boiling water), NOT 80°C (176°F). Always check the source document's context and date: pre-1850 European texts almost always use Réaumur; post-1850 scientific texts progressively shifted to Celsius. Russian popular texts used Réaumur into the early 20th century.
The National Institute of Standards and Technology provides authoritative definitions and conversion factors for all temperature scales including Fahrenheit, Celsius, Kelvin, and Rankine. The NIST Guide to the SI clarifies which scales are part of the International System of Units (Kelvin and Celsius) and which are legacy scales (Fahrenheit, Réaumur, Rankine) — essential context for any work involving historical or non-SI temperature data.
Visit NIST →The Réaumur scale is one of the most historically significant temperature scales in European science. Understanding its origins, use across 18th–19th century European countries, and eventual replacement by Celsius provides essential context for interpreting historical scientific and literary texts. Encyclopaedia Britannica's article on thermometry provides a comprehensive overview of the development of temperature scales from Fahrenheit and Réaumur through to the modern Kelvin scale.
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