Engineers who work with steam tables, jet engines, and refrigeration cycles live in Rankine — the absolute temperature scale that pairs with Fahrenheit the way Kelvin pairs with Celsius. Proposed by Scottish engineer William Rankine in 1859, it starts at absolute zero and uses Fahrenheit-sized degrees, so converting from Celsius takes two hops: add 273.15 to reach Kelvin, then multiply by 9/5. The formula is (°C + 273.15) × 9/5. Type 20 into the Celsius (°C) box and the Rankine (°R) readout shows about 527.67; the bonus boxes give you 293.15 K and 68°F alongside. Water freezes at 491.67°R and boils at 671.67°R — big numbers that look alarming until you remember absolute zero sits at 0°R (−459.67°F). Thermodynamics formulas need an absolute scale to work, which is why Rankine persists in American engineering while the rest of the world uses Kelvin. If a US textbook problem demands Rankine, this is the bridge.

With the pre-filled defaults — Celsius (°C) 0 — the Celsius to Rankine returns Rankine (°R) 491.6700, Kelvin (K) 273.1500, Fahrenheit (°F) 32.0000. Change any input and those results update instantly, so you can see exactly how each number you enter moves the answer.