France measured temperature in Réaumur for over a century — René Réaumur's 1730 scale splits water's freeze-to-boil range into 80 degrees — so converting Fahrenheit into it is a small act of culinary archaeology. The formula is (°F − 32) × 4/9. Type 68 into the Fahrenheit (°F) box and the Réaumur (°Ré) readout shows 16; a 350°F oven translates to about 141.1°Ré. The anchors line up neatly: 32°F (freezing) is 0°Ré and 212°F (boiling) is exactly 80°Ré, since both scales pin the same physical points. Old French cookbooks and winemaking notes quote Réaumur temperatures, which is why a vintage recipe's "25 degrees" means a warm 31.25°C room, not a chilly oven. Réaumur thermometers used alcohol rather than mercury, and the scale's 80-part symmetry appealed to 18th-century French sensibilities before Celsius swept it aside. Obsolete in every lab, it remains deliciously alive in historical kitchens. A 350°F oven reads about 141°Ré, which shows why the scale suited the slow-cooking era: ordinary kitchen temperatures landed in friendly two- and three-digit numbers.

With the pre-filled defaults — Fahrenheit (°F) 32 — the Fahrenheit to Reaumur Converter returns Réaumur (°Ré) 0.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.