Temperature Converter

Temperature Converter — All Scales

Enter a value, choose the input scale, and instantly see all four temperature scales.

Value is below absolute zero for the selected scale.
—Celsius (°C)
—Fahrenheit (°F)
—Kelvin (K)
—Rankine (°R)

All Temperature Scales Explained

Our all-in-one temperature converter handles all four major temperature scales simultaneously: Celsius, Fahrenheit, Kelvin, and Rankine. Simply enter any temperature, select the scale, and the converter instantly calculates the equivalent values in every other unit.

Celsius (°C)

The Celsius scale, developed by Anders Celsius in 1742, is the world's most widely used temperature scale. It defines 0°C as the freezing point of water and 100°C as the boiling point at sea level. Virtually every country except the United States uses Celsius for everyday temperature reporting. It is also the standard for most scientific work outside of thermodynamics.

Fahrenheit (°F)

Proposed by Daniel Gabriel Fahrenheit in 1724, the Fahrenheit scale sets water's freezing point at 32°F and boiling point at 212°F — a 180-degree interval compared to Celsius's 100-degree interval. Fahrenheit is primarily used in the United States for weather, cooking, and medicine. Converting between Fahrenheit and Celsius requires the formula °C = (°F − 32) × 5/9.

Kelvin (K)

The Kelvin scale is the SI absolute temperature scale. Its zero point (0 K = −273.15°C) is absolute zero — the coldest possible temperature. Kelvin uses the same degree interval as Celsius but starts at absolute zero. It is essential for thermodynamic, astrophysical, and quantum physics calculations. The formula is K = °C + 273.15.

Rankine (°R)

The Rankine scale is an absolute temperature scale like Kelvin, but it uses Fahrenheit-sized degrees. Zero Rankine equals absolute zero (−459.67°F). It is used primarily in engineering applications in the United States, particularly in thermodynamics and aerospace engineering. The formula is °R = °F + 459.67, or °R = K × 9/5.

Quick Conversion Formulas

  • °F = (°C × 9/5) + 32
  • K = °C + 273.15
  • °R = (°C + 273.15) × 9/5
  • °C = (°F − 32) × 5/9
  • °R = °F + 459.67
  • °R = K × 9/5

Frequently Asked Questions

What is the difference between Kelvin and Rankine?
Both Kelvin and Rankine are absolute temperature scales starting at absolute zero. The difference is the size of their degrees: Kelvin uses Celsius-sized degrees, while Rankine uses Fahrenheit-sized degrees. Therefore 1 K = 1.8°R. Kelvin is the SI standard; Rankine is used mostly in US engineering.
Which temperature scale is most accurate for science?
The Kelvin scale is the most appropriate for scientific use because it is an absolute scale beginning at absolute zero. Thermodynamic equations require absolute temperature; using Celsius or Fahrenheit would require constant corrections.
What temperature is the same in all four scales?
There is no single temperature value that is numerically identical across all four scales simultaneously. However, −40 is the same in Celsius and Fahrenheit. Absolute zero (0 K = 0°R = −273.15°C = −459.67°F) is a common reference across all scales.
Why does Rankine exist if we already have Kelvin?
Rankine was developed by Scottish engineer William Rankine in 1859 for use alongside Fahrenheit in American engineering. Since US engineers were already using Fahrenheit, Rankine provided an absolute scale compatible with those measurements without having to switch to Celsius-based Kelvin.
How do I convert between all four temperature scales quickly?
The easiest method is to first convert any temperature to Celsius, then derive all others: Fahrenheit = C×9/5+32; Kelvin = C+273.15; Rankine = (C+273.15)×9/5. Our all-in-one converter does all of this automatically the moment you type a value.