What is a Rankine?

The Rankine scale is the absolute version of Fahrenheit, named after Scottish engineer William John Macquorn Rankine (1820–1872). Like Kelvin, Rankine sets 0° at absolute zero, but uses Fahrenheit-sized degrees: 1°R = 1°F (in size, not in offset). Water freezes at 491.67°R and boils at 671.67°R at sea level. The scale is rarely used today except in some American engineering disciplines, particularly in older thermodynamics, refrigeration, and aerospace calculations where Fahrenheit is the working unit. The Rankine relates to Fahrenheit by °R = °F + 459.67 and to Kelvin by °R = K × 9/5. While Kelvin has largely replaced Rankine in modern science, Rankine retains a niche in certain US engineering textbooks and HVAC standards. Its main advantage is allowing absolute-temperature thermodynamic calculations within a Fahrenheit-based engineering context.

Visual reference for how the rankine relates to other temperature units. Each row links to the full converter for that pair.

• US aerospace thermodynamics
• US steam-turbine and power-plant engineering
• Some US industrial combustion calculations

• ✓°R = °F + 459.67.
• ✓°R = K × 9/5. Identical absolute-zero anchor, different degree size.
• ✓Rankine is essentially obsolete outside specific US engineering specialisms.

• ✗Confusing Rankine with Réaumur (another historical scale).
• ✗Using Rankine outside US engineering contexts — nowhere else uses it.
• ✗Writing °R when Réaumur degree is meant — Réaumur is obsolete.