Every Fahrenheit thermometer descends from a Danish astronomer's forgotten scale: around 1702, Ole Rømer defined 0°Rø at freezing brine and 60°Rø at boiling water, and Daniel Fahrenheit later multiplied and shifted those divisions into the scale Americans still use. Converting Fahrenheit back into Rømer uses the formula (°F − 32) × 7/24 + 7.5. Type 68 into the Fahrenheit (°F) box and the Rømer (°Rø) readout shows 18; freezing at 32°F lands on 7.5°Rø, and boiling at 212°F hits exactly 60°Rø. The odd 7.5 offset is the fossil of Rømer's brine-based zero — Fahrenheit kept the structure and moved the goalposts to 32 and 212. Rømer is better remembered for first measuring the speed of light, but his temperature scale quietly shaped every American weather report. This page is a time machine: one input, and you are reading temperatures like an 18th-century Copenhagen observatory. The scale's 60-degree span between brine-freezing and boiling made each Rømer degree relatively large — about 3.4 Fahrenheit degrees apiece.

With the pre-filled defaults — Fahrenheit (°F) 32 — the Fahrenheit to Romer Converter returns Rømer (°Rø) 7.5000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.