Last updated: October 2026
Fahrenheit to Celsius
Fahrenheit-to-Celsius is the most searched temperature conversion because weather, ovens and body temperature are reported in °F in the US and °C nearly everywhere else. The formula has two steps — subtract 32, then scale by 5/9 — because the two scales have different zero points and different degree sizes. For a quick mental estimate, "subtract 30, then halve" lands within a few degrees: 50°F → (50−30)/2 = 10°C, exactly right by luck.
Celsius to Fahrenheit
Going the other way reverses both operations in reverse order: scale first (× 9/5), then shift (+ 32). The anchor points to memorize: 0°C = 32°F (water freezes), 100°C = 212°F (water boils), and the crossover −40° is −40° on both scales — the one temperature where Fahrenheit and Celsius agree. Body temperature is 37°C = 98.6°F, and "room temperature" of 21°C lands at 69.8°F, usually rounded to 70°F on thermostats.
Kelvin and Rankine: the absolute scales
Kelvin is the SI unit and the scientist's scale: 0 K is absolute zero (−273.15°C), the point where molecular motion stops. Celsius and Kelvin degrees are the same size, so converting is just a shift: add or subtract 273.15. Rankine is Kelvin's Fahrenheit-flavored sibling — same zero as Kelvin, but with Fahrenheit-sized degrees: 0°C = 491.67 °R. Both absolute scales matter because many physics and engineering formulas (the ideal gas law, black-body radiation) only work with temperatures measured from absolute zero.
Popular temperature conversions
| Conversion | Answer |
|---|---|
| 50°F in Celsius | 10°C |
| 108°F in Celsius | 42.22°C |
| 0°C in Fahrenheit | 32°F |
| 36°C in Fahrenheit | 96.8°F |
| 62°F in Celsius | 16.67°C |
| 21°C in Fahrenheit | 69.8°F |
| 100°C in Fahrenheit | 212°F |
| 32°F in Celsius | 0°C |
| 0°C in Kelvin | 273.15 K |
| 212°F in Celsius | 100°C |
| −40°F in Celsius | −40°C |
| 98.6°F in Celsius | 37°C |
How temperature conversion works
Length conversion is one multiplication because all length units share a zero. Temperature scales don't: Fahrenheit's 0 is a brine-freezing mixture from 1724, Celsius's 0 is water freezing. So converting takes two operations in the right order — shift, then scale (or scale, then shift, coming back). The converter above routes everything through Kelvin internally: convert to Kelvin first (undoing both the shift and scale of the source unit), then from Kelvin to the target. Below absolute zero (−273.15°C) it refuses, because no such temperature exists — a guard most online converters silently skip.