Fahrenheit to Rankine Converter
Convert °F to °R for ideal-gas, thermodynamics and aerospace calculations done in US customary units.
°R = °F + 459.67
Why It Is Just + 459.67
Rankine was designed as the absolute version of Fahrenheit. The degrees are the same size, so nothing needs rescaling. The only difference is where zero sits: Rankine starts at absolute zero, which is 459.67 Fahrenheit degrees below 0°F.
That number comes from the Celsius definition. Absolute zero is −273.15°C, and −273.15 × 1.8 + 32 = −459.67°F. Because it's derived from an exact definition, 459.67 is exact too. Older textbooks that use 460 are rounding.
Worked Example: Air Density in English Units
What is the density of air at 80°F and sea-level pressure (14.696 psia)? The ideal gas law, ρ = P ÷ (R·T), needs an absolute temperature.
Step 1: Convert to Rankine
Step 2: Convert pressure to lbf/ft²
Step 3: Apply ρ = P ÷ (R·T), with R = 53.35 ft·lbf/(lbm·°R) for air
Air weighs about 0.0735 lb per cubic foot. Plugging in 80 instead of 539.67 gives 0.496 lbm/ft³, almost seven times too dense.
Gas Constants per °R
In English units, each gas's specific gas constant is the universal constant, 1,545.35 ft·lbf/(lbmol·°R), divided by its molar mass. These are the values to pair with a Rankine temperature.
| Gas | Molar mass (lb/lbmol) | R (ft·lbf/lbm·°R) |
|---|---|---|
| Air | 28.965 | 53.35 |
| Nitrogen (N₂) | 28.013 | 55.17 |
| Oxygen (O₂) | 31.999 | 48.29 |
| Carbon dioxide (CO₂) | 44.01 | 35.11 |
| Helium (He) | 4.0026 | 386.09 |
Fahrenheit to Rankine Table
Every °R value is exactly 459.67 above its °F value.
| °F | °R |
|---|---|
| -459.67°F | 0°R |
| -40°F | 419.67°R |
| 0°F | 459.67°R |
| 32°F | 491.67°R |
| 59°F | 518.67°R |
| 70°F | 529.67°R |
| 100°F | 559.67°R |
| 212°F | 671.67°R |
| 500°F | 959.67°R |
| 1,000°F | 1,459.67°R |
| 2,000°F | 2,459.67°R |
| 3,000°F | 3,459.67°R |
Frequently asked questions
Is 460 close enough?
For rough estimates, yes: the error is 0.33°R, under 0.1% at room temperature. Use 459.67 when the result feeds into further calculation or is compared with published data.
Does a temperature change need converting?
No. A rise of 20°F is a rise of 20°R, because the degrees are the same size. Only absolute readings get the 459.67 offset.
Why do some steam tables start at 491.69°R?
English-unit steam tables usually start at the triple point of water, 32.018°F (0.01°C), not at 32°F. Add 459.67 and you get 491.688°R, which rounds to 491.69°R.
How does Rankine compare to kelvin?
Both start at absolute zero, but a kelvin is 1.8 times larger than a degree Rankine: °R = K × 1.8. Use Rankine with US customary units and kelvin with SI units.
Sources
- NIST Special Publication 811, Guide for the Use of the International System of Units (SI): Fahrenheit and Rankine conversion factors.
Related Tools
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Convert Fahrenheit to Celsius.
Convert Fahrenheit to Kelvin.
Convert Kelvin to Celsius.